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U. S. Department of Justice 

JI®, j)| Federal Bureau of Investigation 






PROC€€DINGS 
F TH€ 


. MAY 

% v pm- 




NT €RNRTIONfll 
SYMPOSIUM 


ON TH€ 
RNRLYSIS AND 


D€T€CTION 

OF 

GCPLOSIV6S 




FBI ACADCMY 
QUANTICO, VIRGINIR 
MARCH 29-31,1983 









































Proceedings 
of the 

International Symposium 

on the 

Analysis and Detection of Explosives 


MARCH 29-31,1983 
FBI ACADEMY 
QUANTICO, VIRGINIA 


Sponsored by The Federal Bureau of Investigation 



NOTICE 

This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the 
United States Department of Justice, nor any of their employees, makes any warranty, express or implied, or assumes any legal li¬ 
ability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, 
or represents that is use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or 
service by trade name, mark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommenda¬ 
tion, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do 
not necessarily state or reflect those of the United States Government or any agency thereof. 


Cover: Aerial photograph of FBI Academy by George February. 


II 

A- 601 Wl 




Foreword 


On March 29-31, 1983, the FBI hosted the “International Symposium on the 
Analysis and Detection of Explosives” in the Bureau’s Forensic Science Research 
and Training Center at the FBI Academy at Quantico, Virginia. The Symposium 
was attended by 175 people from academia, Federal, state and local law enforce¬ 
ment forensic laboratories, the military and the explosives industry. 

The 57 papers presented, covering all aspects of current R&D in the field of ex¬ 
plosive analysis and detection, represented many new and interesting techniques. 

This symposium was an outgrowth from the need to bring together scientists in 
the field who share common interests and problems in explosive analysis and detec¬ 
tion for the purpose of enhancing dialog in the overall goal of controlling the use of 
explosives by terrorists and other criminals. The FBI is deeply appreciative that so 
many organizations and agencies were willing to share their expertise to help tackle a 
problem of international proportions. 

I have received many comments on the level of professionalism and high stand¬ 
ards of the meeting and its significance to the field of analytical chemistry. Indeed, 
these proceedings which are a compilation of the 57 papers presented, represent a 
milestone in the field. 

On behalf of the FBI Laboratory, I would like to personally extend my thanks 
to the program committee, the individuals who presented papers and the other par¬ 
ticipants for making the Symposium what I believe was an overwhelming success. 

James H. Geer 
Assistant Director 
in Charge 
FBI Laboratory 


III 
















































Symposium Steering Committee 


Federal bureau of investigation 
Charles E. Calfee 
Terry L. Rudolph 
Dennis J. Reutter 
Cecil E. Yates 

BUREAU OF ALCOHOL TOBACCO AND FIREARMS 
Daniel D. Garner 


Session Chairmen 

FlIGH PERFORMANCE LIQUID CHROMATOGRAPHY METHODS 
Ira Krull, Northeastern University 

GENERAL ANALYSIS 

Elliott B. By all, BATF 

INSTRUMENTAL ANALYSIS 

A lexander Beveridge, R CMP 
Shmuel Zitrin, Israel Police 

MASS SPECTROMETRY METHODS 

Richard Saferstein, New Jersey State Police 

High performance Liquid Chromatography 
J. B. E. Lloyd, Home Office, England 

EXPLOSIVE DETECTION 

Frank Conrad, Sandia Laboratory 
Charles E. Calfee, FBI 


V 

























Contents 


Foreword iii 

SYMPOSIUM STEERING COMMITTEE AND SESSION CHAIRMEN v 

KEYNOTE ADDRESS 

Jehuda Yinon, Weizmann Institute of Science, Rehovot Israel 1 

SYMPOSIUM PRESENTATIONS 9 

High performance Liquid Chromatography Methods 

1. “The Trace Analysis for Explosives and Related Compounds Via Liquid Chromatography— 

Electrochemistry (LCEC)’’ 

I. S. Krull, M. Malinouski and C. Selwka 11 

2. “Screening for Organic Explosives Components by High Performance Liquid 

Chromatography With Detection At A Pendant Mercury Drop Electrode,” 

J. B.F. Lloyd 31 

3. “Detection and Analysis of Polynitrophenols in Water by Reversed-Phase Ion-Pair Liquid 

Chromatography, ’ ’ 

John C. Hoffsommer and Donald J. Grover 41 

4. “Liquid Chromatography/Electrochemistry Detection of Explosives,” 

Peter Kissinger 45 

5. Symposium paper no. 5 not submitted. 49 

General Analysis 51 

6. “Identification of Reaction Products in Explosive Residues,” 

A. D. Beveridge, W. R. A. Greenlay, and/?. C. Shaddick 53 

7. “Identification and Tracing on Non-Explosive Components in Explosion,” 

Harold Messier 59 

8. “Explosive Analyses Kit,” 

Lyle O. Malotky and Steven A. Downes 63 

9. “Organic Solvent Extracts of Explosive Debris: Clean-Up Procedures,” 

Richard A. Strobel and Richard Tontarski 61 

10. “A Scheme for the Analysis of Explosive Residues,” 

Terry L. Rudolph 71 

11 . “Nonideal Detonation Behavior of Suspended Explosives As Observed From Unreacted 

Residues,” 

J. Edmund Hay, Yael Miron, and Richard W. Watson 79 


VII 


Instrumental Methods 91 

12. “Instrumental Techniques Utilized in the Identification of Smokeless Powders,” 

Richard E. Meyers and John A. Meyers 93 

13. “The Use of Multiple Detection in the Gas Chromatographic Analysis of Organic Nitro 

Compounds and Explosives (GC-ECD/PID).” 

I. S. Krull, M. Swartz, and K. H. Xie 107 

14. “Determination of Nitro Explosives by GC Utilizing an On-Column Capillary Injector,” 

Zelda Pen ton 123 

15. “Thermal Analysis of Pyrotechnics and Explosives,” 

John A. Conk ling 129 

16. “Identification of Two Rare Explosives,” 

Shmuel Zitrin, Shmuel Kraus, and Baruch Glattstein 137 

17. “Identification, Structural Determination and Quantitation of an Unknown Explosive,” 

Tung-HoChen 143 

18. “Analysis of an Unusual Explosive: Methods Used and Conclusions Drawn from Two Cases,” 

Dennis J. Reutter and Terry L. Rudolph 149 

19. “Description of a Nitro/Nitroso Specific Detector for the Trace Analysis of Explosives,” 

D. H. Fine 159 

20. “Applications of the Nitro/Nitroso Specific Detector to Explosive Residue Analysis,” 

E. U. Goff, W. C. Yu, and D. H. Fine 169 

21. “X-Ray Photoelectron Spectroscopic (XPS) Detection And Identification of Explosive 

Residues,” 

J. Sharma 181 

22. “Characterization and Identification of Water-Soluble Explosives by Light Microscopy,” 

John H. Kilbourn 187 

23. “Identification of Water-Soluble Explosives and their Post-Blast Residues by Ion 

Chromatography,” 

Dennis J. Reutter and Richard C. Buechele 199 

24. “The Use of Ion Chromatography in the Analysis of Water Gel Explosives,” 

D. J. Barsotti and R. M. Hoffman 209 

25. “The Characterization of Some Low Explosive Residues by Ion Chromatography,” 

Terry L. Rudolph 213 

26. “Identification of Explosives Containing Alkylammonium Nitrates by TLC,” 

William Dietz, George Peterson and LeRoy Stewart 221 

Mass Spectrometry methods 225 

27. “Analysis of Explosives by Liquid Chromatography/Mass Spectrometry,” 

J. Yinon 227 

28. “The Analysis of Post Detonation Carbon Residues by Mass Spectrometry,” 

A. S. Cumming and K. P. Park 235 

29. “On-Line Computer Search System Applied to Explosives,” 

Harold Messier 241 

30. “Identification of Smokeless Powders and Their Residues By Capillary Column Gas 

Chromatography/Mass Spectrometry,’’ 

Roger M. Martz, T. O. Munson, and Lynn D. Laswell 245 

31. “Fingerprints of Detonation Products from Navy Explosives,” 

C. A. Heller, J. H. Johnson, E. D. Erickson, S. R. Smith, L. A. Mathews 255 

32. “The Analysis of Trace Levels of Explosives by Gas Chromatography/Mass Spectrometry,” 

A. S. Cumming and K. P. Park 259 


VIII 


33. “Analysis of Explosives and Explosive Residues with Ion Mobility Spectrometry,” 

G. E. Spangler, J. P. Carrico, and S. H. Kim 267 

High Performance Liquid Chromatography Methods 283 

34. ‘‘The Analysis of Ethyleneglycolmononitrate and Monomethylamine Nitrate in Commercial 

Blasting Agents and Post Blast Samples,” 

R. J. Prime and Juerg Krebs 285 

35. “Analysis of Explosives by FTIR,” 

Terry Mills and Randall H. Riddell 289 

36. “Analysis of Smokeless Powders by HPLC,” 

Edward C. Bender 309 

37. “Analysis of Trace Explosives by Microbore HPLC,” 

Jeff Bowermaster and Harold M. McNair 321 

38. “Determination of Nitrate Esters, Nitramines, Nitroaromatics and the Metabolites in 

Biological Fluids by Liquid Chromatography with a Nitro/Nitroso Specific Detector,” 

W. C. Yu, E. U. Goff, and D. H. Fine 329 

39. “Explosive Residue Detection by HPLC using an Electrochemical Detector,” 

R. C. Briner and C. R. Longwell 341 

40. “The Evaluation of FTIR as a Detector for the HPLC Analysis of Explosive Residues,” 

Richard A. Strobel, Richard Tontarski, Antonio Cantu, and Willard Washington 349 


Miscellaneous methods 365 

41. “Proton NMR Characterization of Explosives,” 

Hans-Dieter Schiele and Gottfried Vordermaier 367 

42. “Radiofrequency Resonance Absorption Spectroscopic (RRA) Methods For the 

Detection and Analysis of Explosives,” 

William L. Rollwitz and J. Derwin King 371 

Explosive detection 385 

43. “Program on Explosives Vapor Detection” 

Frank J. Conrad 387 

44. “Temperature Dependence of Absorption Effects of Explosive Molecules,” 

Phyllis K. Peterson 391 

45. “The Sorption of Explosives on Human Hair,” 

D. F. Wardleworth and S. A. Ancient 397 

46. “A Novel Method for the Recovery of Volatile Explosive Traces,” 

D. F. Wardleworth and S. A. Ancient 405 

47. “The Instantaneous Detection of Explosives by Tandem Mass Spectrometry,” 

William R. Davidson and John E. Fulford 409 

48. “A Man-Portable GCMS for Explosives Detection,” 

Russell C. Drew and Christopher Stevens 419 

49. Symposium Paper No. 49 not submitted. 429 

50. “Sampling of Explosives With Multiple, Portable Preconcentrating Cartridges,” 

Ralph J. Sullivan and Gary W. Watson 431 

51. “Remote Detection of Explosives Using Trained Canines,” 

James C. Smith 441 


IX 


52. “The Scientific Development of an Efficient Detector Dog Through Olfactory and 

Behavioral Modification,’’ 

Edward Dean 451 

53. “Indicator Tubes for the Detection of TNT,” 

E. D. Erickson, S. R. Greni, and D. J. Burdick 459 

54. “The Tagging of Explosives; The New Swiss Law on Explosives; Development 

Achievements and First Experiences,” 

J. Scharer 463 

55. “Internal Standard Chemical Labeling on Intact Explosives and the Subsequent On-Line 

Thin Layer Flame Ionization of Novogram Quantities of These Standards in the Spent 
Explosive Residues,” 

J. Bruce Schlegel 471 

56. “The Analysis of Organic Components in Gunshot Residues,” 

J. M. F. Jane I. Douse and K. A. O’Callaghan 475 

57. “New Measurement Studies On the Effects of IED,” 

Werner Wildner 485 

Special Presentation 495 

58. “Highspeed Photography of Clandestine Explosive Devices,” 

Paul M. Dougherty 497 

Paper Which Was Submitted but Author Unable to Attend 501 

59. “Detection of Improved Explosive Devices, A System for Ensuring Mail Safety,” 

D. W. Williams 503 


X 


KEYNOTE ADDRESS 


NEW HORIZONS IN MASS SPECTROMETRY FOR THE ANALYSIS 

OF EXPLOSIVES 

Jehuda Yinon 

The Weizmann Institute of Science 
Rehovot, Israel 


Mr. Chairman, Ladies and Gentlemen: 

First, I would like to thank our host, the Federal Bureau of Investigation, and in particular the or¬ 
ganizing committee, for the initiative and the organization of this important symposium; and, I would 
like to express my deep appreciation for being invited as the keynote speaker. 

This meeting is important because it presents a unique forum where scientists from around the world 
are able to present, to listen to, and to discuss new approaches, new applications, new methods and new 
instrumentation in the field of analysis and detection of explosives. 

Having seen the number of papers in the program and their topics, I believe that this meeting will be 
another milestone in this one area of the battle against crime and terrorism. 

Our efforts should be concentrated toward the common goal of creating an international collabora¬ 
tion in this field. Exchange of information involving all scientists active in the analysis and detection of 
explosives is vital to the successful achievement of this goal. 

The subjects of this collaborative effort should include the development of new instrumental meth¬ 
ods and their evaluation; the improvement of established techniques; and the evaluation—for the analysis 
of explosives—of new techniques which have already proved to be successful in other fields. A typical ex¬ 
ample of this last group has been the introduction of chemical ionization mass spectrometry for the analy¬ 
sis of explosives, about 9 years ago, which was the result of a collaborative effort between our laboratory 
at the Weizmann Institute of Science and the Israeli Police. 

Several new developments in mass spectrometry have appeared during the last few years and have 
been very successful in various analytical applications. These are: 

(1) On-line high performance liquid chromatography—mass spectrometry (LC/MS). 

(2) On-Line micro liquid chromatography-mass spectrometry (Micro LC/MS). 

(3) Tandem mass spectrometry (MS/MS). 

(4) Several novel ionization techniques: 

(a) Laser desorption (LD). 

(b) Fast atom bombardment (FAB). 

(c) Secondary ion mass spectrometry (SIMS). 

Initial experimentation with some of these techniques for the analysis of explosives has already been 
done, but a complete evaluation has still to be carried out. 

I would like to describe one of these techniques: MS/MS, its principles, the instrumentation and 
possible applications in our field. 

This technique has been pioneered by John Beynon [Bozorgzadeh, Morgan and Beynon (1978)] in 
the United Kingdom and by Fred McLafferty [Bente, III and McLafferty (1980)], Graham Cooks [Cooks 
and Glish (1981)] and Chris Enke [Yost and Enke(1979)] in the United States. 

As can be understood from the technique’s name, MS/MS, we are talking about the combination of 
two mass spectrometers. The combination of two techniques is well known from GC/MS and recently 
from LC/MS which consist of a combination of separation and identification techniques. MS/MS con¬ 
sists of two mass spectrometers in tandem with a reaction cell between them. A schematic illustration of 
an MS/MS is shown in Figure 1. The sample can be one single compound or a mixture. Accordingly we 
would use either electron impact (El) or chemical ionization (Cl) or any other ionization method. 


1 


ION SOURCE 



Figure 1. Schematic illustration of an MS/MS system. 

The first mass analyzer separates the ions produced in the source. We select the primary ion to enter 
the reaction cell. For example, if the sample is a mixture, we will chose the MH + ion of one of the compo¬ 
nents to enter the reaction cell. In the cell the primary ion beam collides with an inert gas such as helium, 
argon or nitrogen, resulting in collision-induced dissociation (CID) of the selected ion. This is also called 
collisionally activated dissociation (CAD). 

There are two types of CID in the reaction cell, depending on the type of the first mass analyzer: 

(1) High-energy collisions if the first mass analyzer is a magnetic sector one. The primary ion has an 
energy of several KeV. 

(2) Low-energy collisions if the first mass analyzer is a quadrupole. The primary ion has an energy 
of 0-100 eV. 

While in high-energy CID, the collisions of the ion with the inert gas transforms some of the transla¬ 
tional energy of the ion into internal excitation energy, in low energy CID, the transfer of momentum 
plays a more important role than the transfer of energy; therefore larger molecules such as nitrogen are 
more effective than small atomic species such as helium, as collision gas. 


2 













The fragment ions produced in the reaction cell are mass analyzed by the second mass analyzer and 
recorded. This secondary mass spectrum provides a “fingerprint” of the primary ion beam. 

There are several types of MS/MS configurations: 

(1) Reversed-geometry double-focusing mass spectrometer (CID-MIKES). 

(2) Triple quadrupole system. 

(3) Magnetic sector (B) and quadrupole (Q) combination (hybrid): 

(a) BQQ 

(b) QQB 

(4) Triple sector combination: 

(a) BEQQ 

(b) EBQQ 

(c) BEB 

(5) Four sector combination, which includes two magnetic sector analyzers (B) and two electrostatic 
analyzers (E). 

The reversed geometry double-focusing mass spectrometer uses the magnetic field as the first mass 
analyzer and the electrostatic analyzer as second mass analyzer. This particular configuration is called 
MIKES: mass analyzed ion kinetic energy spectrometry; because mass selection (by momentum analysis) 
is followed by an ion kinetic energy analysis of the product ions. The mass scale of the fragment ions 
formed in a MIKE spectrum is a linear function of the electric sector voltage. Figure 2 shows schematical¬ 
ly the ion optical system of such a spectrometer. 

The triple quadrupole system, Figure 3, consists basically of a tandem quadrupole mass spectrometer 
(first and third quadrupoles). The second quadrupole has only an R.F. voltage (without D.C. voltage) 
and serves therefore only as an ion focusing device. The reaction cell is located between the rods of this 
quadrupole. It has been found that when using a quadrupole mass analyzer, an additional quadrupole fo¬ 
cusing device is needed to focus the ions in the reaction cell. This is also necessary in hybrid combinations. 

In the triple quadrupole system the collisions of the primary ions with the neutrals are low energy col¬ 
lisions (0-100 eV). Figure 4 shows an example of a BEQQ triple sector system. This system has several re¬ 
action cells (collision cells) in different parts of the instrument, thus enabling a variety of experiments. 
Collision cell 2, between the magnetic and electrostatic analyzers is suitable for high energy CID, while 
collision cell 3, after the deceleration lens, is suitable for low energy CID experiments. 

Several experiments can be carried out with an MS/MS: 

(1) Daughter experiment: allows a survey of specific compounds in complex organic mixtures. Each 
component of the mixture is represented by its molecular ion (in El) or by its MFD ion (in Cl). Each of 
these chosen ions undergoes CID in the reaction cell and is identified by its CID mass spectrum at the col¬ 
lector of the second mass analyzer. 


P’B LIT 

(VARjABCEJ 


TOTAL i QN 


\ 


ELECTRpN 
MULT i PLIf P * 1 



Figure 2. Ion optical system of a MIKE-CID spectrometer [Morgan et at. (1978)]. 


3 
























CUTAWAY VIEW OF 
TRIPLE QUADRUPOLE MS/MS SYSTEM 


ION SOURCE QUADRUPOLE 1 QUADRUPOLE 2 QUADRUPOLE ] 


ELECTRON 

MULTIPLIER 


IONIZATION- 


1 si STAGE 

MASS 

► SEPARATION- 


COLLISION 
• FOCUSSING 


2nd STAGE 

MASS 

► SEPARATION 


• DETECTION 


SAMPLE 

INLETS 


IONIZER 


ANALYZER 


'TURBOMOLECULAR ' 
PUMPS 


Figure 3. Triple quadrupole system [Slyaback and Story (1981)] 


Magnet 


Alpha Slit 




ESA 


Collector Slit — 



Deceleration 

Lens 


Source Slit • 
El/Cl Source [ 



Collision Cell 1 


-I I Detector 1 

= 1 = 

r ni Collision 
! Cell 3 

_ I (RF Quad.) 


Quadrupol- 

Analyzer 

Detector 2 


Figure 4. BEQQ triple sector system [Finnigan MAT (1982)] 


4 






























































































































(2) Parent experiment: the first mass spectrometer is scanned while the second is set at a specific 
mass. This experiment identifies all parent ions that decompose to a predetermined daughter ion which is 
being detected by the second mass spectrometer. This experiment will detect all compounds that decom¬ 
pose to a common fragment. For example, trinitroaromatic compounds could be identified by the NO + 
fragment ion, while nitrate esters by the N0 2 fragment ion. 

(3) Neutral loss experiment: the mass analyzers are set to detect a constant neutral loss. For exam¬ 
ple, the first mass analyzer is scanned from m/z 37 to 300, at the same time as the second mass analyzer is 
scanned from m/z 20 to 283. In this example the neutral loss of 17 units may represent a series of nitro¬ 
compounds losing OH. In a similar way one might want to look for compounds which have a neutral loss 
of NO or N0 2 . Neutral loss experiments can be done in a much easier way on a triple quadrupole instru¬ 
ment because quadrupoles are more suited for computer control. 

Another use of MS/MS is structure identification and determination of fragmentation patterns. 
Fragmentation patterns of RDX and HMX have been determined by MS/MS using a MIKE-CID spec¬ 
trometer [Yinon, Harvan and Hass (1982)]. It is well known that the mass spectrometry of RDX and 
HMX poses some problems [Yinon (1982)], because a whole series of fragment ions are produced even in 
the Cl mass spectra. The origin of many of these fragments was difficult to explain, and therefore it was 
difficult to determine fragmentation patterns. The CID mass spectrum is related to the primary ion struc¬ 
ture (or precursor ion structure) in the same way as the El mass spectrum is related to the molecular struc¬ 
ture. Hence the similarity between CID and El spectra. 

Figure 5 shows the MIKE-CID spectrum of the MH + ion at m/z 297 in HMX in the Cl mode using 
methane as reagent gas. Such spectra were recorded for almost all the ions of RDX and HMX in El, Cl 


898848. 


PEAK SPECTRUM 

07/87/81 3:53:00 

SAMPLE. HMX HPCI M/Z 297 CIDM1KES 

N1080< 7031.0.050 U I., 0.00 T 

MAIN DATA + <1 TO 51 


DATA: Z81I232 II 
CALI: Z811232 12 


V1MD0V SIZE 0.t 
REF. MASS 296.844 



297 



Figure 5. MIKE-CID spectrum of the MH + ion at m/z 297 in HMX in the Cl mode with methane. 


5 















and negative-ion Cl. Fragmentation maps, like the one shown in Figure 6, were obtained. It was found 
that the adduct ions (M + NO) + and (M + N0 2 ) + are the precursors of a large number of the fragment 
ions observed in the mass spectra of RDX and HMX 

Although MS/MS has been applied to a variety of analytical fields [Henion et al. (1982), Bateman et 
al. (1982), Hunt et al. (1982)], it has not yet been applied to the analysis of explosives. 

The main features of MS/MS are: specificity, sensitivity and fast response. Therefore, the uses of 
this technique in residue analysis and detection of explosives seem obvious: 

In residue analysis we might want to use one of the larger instruments, for example a hybrid one, 
with medium resolution, for the identification of explosive residues in debris. We would do either parent 
or daughter experiments. For detection of hidden explosives we would use a small computer controlled 
triple quadrupole system having a high pressure source or some molecular separation device which would 
enable the monitoring of large amounts of air. We would program such an MS/MS to do either a parent 
experiment to monitor fragment ions specific to explosives or to monitor neutral losses specific to explo¬ 
sives. 

Those who have the instrumental know-how and the appropriate facilities can mount their own 
MS/MS instruments. Others can buy them, they are already commercially available; but they are very ex¬ 
pensive. The British writer Samuel Butler said already, about a century ago: “Though wisdom cannot be 
gotten for gold, still less can it be gotten without it”. The need for money in research is not new, and to¬ 
day more than before: as analytical instrumentation becomes more sophisticated, it becomes more ex¬ 
pensive. Therefore, collaboration becomes more and more important. I believe that we should try to in¬ 
crease the interest of scientists from the academic world in our subjects, especially those who are using 
novel analytical techniques; and we should increase international collaboration in order to avoid duplica¬ 
tion of efforts and to enhance research and development. 

(m +no 2 )* 


268 



6 







Finally, let me take this opportunity 10 make two suggestions which, I think, should be discussed 
during the following few days: 

First, to establish an association or society. The field of analysis and detection of explosives has al¬ 
ways been a small subdivision of forensic sciences or other disciplines. 1 believe that this field has now be¬ 
come, because of its importance, an independent field. So now is the time to create an International Asso¬ 
ciation for the Analysis and Detection of Explosives. 

The second suggestion is to establish that these International Symposia be held on a permanent basis 
every 3 years and in a different country. I propose to host the next symposium in 3 years at the Weizmann 
Institute of Science in Rehovot, Israel. 

I believe that the establishment of an association, together with periodical symposia, will bring more 
people in the field of analysis and detection of explosives and will increase large scale collaboration. 


REFERENCES 

Bateman, R. H., Green, B. N. and Smith, D. C. 
(1982). A new instrument for the analytical ap¬ 
plication of MS-MS. American Society for 
Mass Spectrometry. 30th Annual Conference 
on Mass Spectrometry and Allied Topics, 
Honolulu, Hawaii. Abstracts, pp. 516-517. 

Bente, III, P. F. and McLafferty, F. W. (1980). 
Analytical applications of two-dimensional 
mass spectrometry. In: Mass Spectrometry (C. 
Merritt, Jr. and C. N. McEwen, editors). Mar¬ 
cel Dekker, Inc., New York, pp. 253-285. 

Bozorgzadeh, M. H., Morgan, R. P. and Bey non, 
J. H. (1978). Application of mass-analysed ion 
kinetic energy spectrometry (MIKES) to the 
determination of the structures of unknown 
compounds. Analyst 103: 613-622. 

Cooks, R. G. and Glish, G. L. (1981). Mass Spec¬ 
trometry/mass spectrometry. Chem. Eng. News 
59: 40-52. 

Finnigan MA Tcatalog D 2/0858, August 1982 

Hen ion, J. D., Skrabalak, D. S. and Thomson, 
B. A. (1982). TLC/MS/MS of drugs in biologi¬ 
cal samples. American society for Mass Spec¬ 
trometry. 30th Annual Conference on Mass 
Spectrometry and Allied Topics, Honolulu, Ha¬ 


waii. Abstracts, pp. 792-793. 

Hunt, D. F., Giordani, A. B., Rhodes, G. and 
Herold, D. A. (1982). Mixture analysis by tri¬ 
ple—quadrupole mass spectrometry: Metabolic 
profiling of urinary carboxylic acids. Clin. 
Chem. 28: 2387-2392. 

Morgan, R. P., Bey non, J. H., Bateman, R. H. 
and Green, B. N. (1978). The MM-ZAB-2F 
double-focusing mass spectrometer and mike 
spectrometer. Int. J. Mass Spectr. and Ion 
Phys. 28: 171-191. 

S/ayback, J. R. B. and Story, M. S. (1981). 
Chemical analysis problems yield to quadrupole 
MS/MS. Ind. Res. Devel. February 
1981: 128-134- 

Yinon, J., Harvan, D. J. and Hass, J. R. (1982). 
Mass spectral fragmentation pathways in RDX 
and HMX. A mass analyzed ion kinetic energy 
spectrometric/collisional induced dissociation 
study. Org. Mass Spectr. 17: 321-326. 

Yinon, J. (1982). Mass spectrometry of explo¬ 
sives: Nitro compounds, nitrate esters, and 
nitramines. Mass Spectr. Reviews. 1: 257-307. 

Yost, R. A. and Enke, C. G. (1979). Triple quad¬ 
rupole mass spectrometry for direct mixture 
analysis and structure elucidation. Anal. Chem. 
51: 1251A-1264A. 


7 























































SYMPOSIUM PRESENTATIONS 

HIGH PERFORMANCE LIQUID 
CHROMATOGRAPHY METHODS 











































THE TRACE ANALYSIS FOR EXPLOSIVES AND RELATED COMPOUNDS 
VIA LIQUID CHROMATOGRAPHY-ELECTROCHEMISTRY (LCEC) 


I. S. Kru/l*, C. Selavka, and X-D. Ding 
Institute of Chemical Analysis 
Northeastern University 
360 Huntington Avenue 
Boston, Massachusetts 02115 
and 

K. Bratin and G. Forcier 
Analytical Research Department 
Pfizer, Inc. 

Groton, Connecticut 06340 


ABSTRACT. Although explosives and related organic nitro compounds have 
now been analyzed via reductive liquid chromatography-electrochemistry (LCEC) 
methods, it is generally acknowledged that oxidative LCEC could not be at all 
compatible with this class of compounds. That is, organic nitro derivatives are al¬ 
ready in their highest oxidation state, and thus could not readily be detected via 
oxidative LCEC. We have now developed a post-column, on-line, real-time pho- 
tolysis/derivatization approach that generates inorganic nitrite from virtually all 
explosives and organic nitro compounds after these elute from the analytical high 
performance liquid chromatography (HPLC) column. This inorganic nitrite is then 
detected via conventional thin-layer flow-through electrode detection in LCEC, 
using single and dual cells in the oxidative and/or reductive modes. These newer 
methods of trace analysis for explosives have now been applied to mixtures of such 
standards, nitroaromatics, nitro polycyclic aromatic hydrocarbons, nitro drugs, 
organic nitrate esters, and related nitro derivatives. We have determined calibra¬ 
tion plots for a large number of explosives using flow injection analysis, photo- 
lysis-EC, as well as HPLC-photolysis-EC (HPLC-hv-EC) methods. At the same 
time, we have determined minimum detection limits (MDLs) for a large number of 
these compounds, suitable HPLC separation conditions using reversed phase 
methods, and have utilized dual electrode response ratioing in order to improve 
analyte identification. At the same time, it has been possible to apply these overall 
methods of analysis to certain real world samples of post-blast debris extracts, 
wherein the selectivity and specificity of the overall HPLC-hv-EC methods are 
readily and fully demonstrated. It is suggested that these trace organic analysis ap¬ 
proaches for explosives should be readily adaptable and applicable to a large num¬ 
ber of other real-world samples in other laboratories. 


INTRODUCTION [11 

Most commonly used explosives contain the ni¬ 
tro (N0 2 ) group somewhere within their struc¬ 
tures, usually bonded directly to either carbon, ni¬ 
trogen, or oxygen atoms (C-NCL, N-N0 2 , or 
0-N0 2 ). Indeed, most explosives contain more 
than one nitro group per molecule of the com¬ 
pounds. Although most of the early work on the 


analysis of explosive materials utilized gas chro¬ 
matography (GC), with a wide variety of suitable 
and often selective/sensitive detectors, within the 
past decade or so, much of the emphasis in such 
analyses has shifted towards the utlization of high 
performance liquid chromatography [Yinon 
(1977), Yinon and Zitrin (1981), Krull and Camp 
(1980), Krull (1983), Krull et al. (1981), Bratin et 
al. (1981), Aim et al. (1978), FBI Academy Sym- 


11 


posium (1983)]. Already, a large number of selec¬ 
tive or general type detectors for HPLC have been 
shown to be suitable for the trace analysis of com¬ 
plex mixtures of explosives, including: ultravio¬ 
let-visible (UV-V1S); electron capture detection 
(ECD); mass spectrometry (MS); Thermal Energy 
Analysis (TEA); reductive electrochemical detec¬ 
tion (EC); and others. However, there remain cer¬ 
tain quite significant disadvantages inherent with¬ 
in each of these detection approaches. Thus, 
UV-V1S is often not selective enough for explo¬ 
sives alone, and it is not generally sensitive enough 
either; ECD is no longer commercially available, 
and it is not easily compatible with reversed phase 
HPLC solvents; MS can be used as an LC detec¬ 
tor, but it tends to be very expensive, difficult to 
operate routinely, and requires sophisticated 
operator training and/or experience; TEA is 
somewhat selective for organic nitro compounds, 
but it will respond to other classes, it is not at all 
compatible with aqueous based reversed phase 
HPLC separations, and it is very expensive as a 
routine HPLC detector goes; and finally, reduc¬ 
tive EC has only been utilized by very few workers 
thus far. Reductive EC can, at times, present seri¬ 
ous operational problems, especially at the trace 
levels of analysis, where oxygen in the sample and 
mobile phase can interfere with the analyte of in¬ 
terest. However, it is clear today that reductive 
LCEC is becoming more and more popular and 
routinely used as a method of trace organic/inor¬ 
ganic analysis, and thus it may yet become a meth¬ 
od of choice for various explosives and organic ni¬ 
tro compounds. Still, at the present time, oxida¬ 
tive liquid chromatography-electrochemistry 
(LCEC) or HPLC-EC is the more widely used and 
preferred mode of electrochemical detection in 
HPLC [Krull et al.{ 1983a), Shoup et al. (1982), 
Krull et al. (1983b), Roston et al. (1982)]. Clearly, 
nitro derivatives, such as the explosives studied 
here, are not directly amenable to oxidative LCEC 
approaches, since they are already in their highest 
oxidation state. However, there was sufficient 
evidence and encouragement in the literature to in¬ 
dicate the possibility of using oxidative LCEC for 
inorganic nitrite (NCK), perhaps generated 
on-line, post-column, in real-time, from suitable 
precursor organic nitro compounds [Krull and 
Lankmayr (1982), Lefevre et al. (1982), Snider 
and Johnson (1979), Sherwood and Johnson 
(1981), Scholten et al. (1980), Green et al. (1977), 
Iwaoka and Tannenbaum (1976), Fogg et al. 
(1982)]. 


Oxidative LCEC has long been used for the 
trace determination of inorganic nitrite, using ion 
chromatography, ion exchange HPLC, or 
paired-ion HPLC [Davenport and Johnson 
(1974), Molnar et a/.(1980), Stevenson and Harri¬ 
son (1981), Bratin (1981)]. Thus, there was little 
question that nitrite was indeed amenable to oxi¬ 
dative LCEC approaches, with working potentials 
of -(-1.2V or below, and that dual electrode EC 
detection was another approach that could even¬ 
tually be utilized for explosives. The overall suc¬ 
cess of this newer approach for explosives there¬ 
fore relied on the release of inorganic nitrite from 
suitable organic nitro derivatives, perhaps via a 
photohydrolysis/photolysis type reaction for de- 
rivatization, after the HPLC separation step be¬ 
fore the oxidative EC detection step(s). Most of 
the literature utilizing photohydrolysis derivatiza- 
tions in HPLC have involved the formation of ni¬ 
trite from various N-nitroso compounds, fol¬ 
lowed by analysis of the nitrite by a Griess Test or 
alternative HPLC detection methods [Snider and 
Johnson (1979), Sherwood and Johnson (1981), 
Scholten et al. (1980), Green et al. (1977), Iwaoka 
and Tannenbaum (1976)]. In essence, the photo¬ 
conductivity detector for HPLC now marketed by 
Tracor Corporation (Austin, Texas) involves pho¬ 
tolysis/photohydrolysis reactions on various or¬ 
ganic compounds, including N-nitroso or organo- 
halogens, followed by detection of the inorganic 
anions once formed via an on-line conductivity 
detector [Popovich et al. (1979), McKinley 
(1981)]. In almost all of this work yet described 
with on-line, real-time, photohydrolysis reactions 
leading to the formation of inorganic anions, vir¬ 
tually nothing had been done emphasizing organic 
nitro compounds. There has been a suggestion in 
the work of Snider and Johnson in the use of a 
photoelectroanalyzer for N-nitroso compounds, 
that organic nitro compounds were often seen as 
interferents in the primary analysis. That is, at 
least some nitro derivatives were shown to lead to 
the presumed formation of nitrite via a photo¬ 
hydrolysis reaction, after the HPLC separation, 
and this could then lead to a false positive in the 
direct analysis for N-nitroso compounds [Snider 
and Johson (1979)]. However, nothing further 
was ever described or discussed in this work or 
that of others using photohydrolysis or photolysis 
in HPLC determinations of N-nitroso com¬ 
pounds. Nevertheless, all of the available litera¬ 
ture seemed to strongly suggest that HPLC-pho- 
tolysis-EC (HPLC-hv-EC) might very well serve 


12 


as a useful and practical approach for the trace 
analysis and speciation of a wide variety of explo¬ 
sives and other organic nitro compounds/ana¬ 
lytes. At the same time, these methods could be 
adapted to other classes of organic compounds, 
wherein these can release an inorganic anion via 
photolysis that could then be detected by EC 
means. 

Although our initial interest in the use of 
HPLC-hv-EC was directed to the trace analysis 
of explosives, it rapidly became apparent that 
these basic methods could just as readily be used 
with a wide variety of other organic nitro com¬ 
pounds, besides explosives. We therefore describe 
here our overall analytical results for a variety of 
commonly used explosives, including: 2,4,6-trini¬ 
trotoluene (TNT); dinitrotoluene (DNT); nitrogly¬ 
cerin (NG); 1,3,5—trinitro—1,3,5-triazacyclo- 
hexane (RDX); 2,4,6,N-tetranitro-N-methyl- 
aniline (TETRYL). In addition, we have applied 
HPLC-hv-EC to certain simple aliphatic nitrate 
esters (R-0-N0 2 ), such as w-propyl nitrate and 
/sopropyl nitrate, as well as to a particular coro¬ 
nary vasodilator, isosorbide dinitrate (ISDN). 
Finally, we have tried to apply these analytical 
methods to various aromatic nitro derivatives, 
such as mono-nitrotoluene isomers, dinitro¬ 
toluene isomers, and certain nitro derivatives of 
polycyclic aromatic hydrocarbons (nitro-PAHs). 
We have also attempted to define what inorganic 
anions might interfere in these HPLC-hv-EC 
analyses for organic nitro compounds, and which 
inorganic anions present no potential problems as 
interferents. Indeed, these results suggest that 
there will be several other classes of organic com¬ 
pounds that will be shown to produce significant 
responses in HPLC-hv-EC approaches. Im¬ 
proved analyte identification and compound spe¬ 
cificity is possible via the use of appropriate dual 
electrode EC approaches, wherein these are feasi¬ 
ble/practical for the particular inorganic/organic 
anion generated by the photolysis/photohydroly¬ 
sis reaction. In addition, these results are shown to 
provide a flow injection analysis method, in the 
absence of an initial HPLC separation, utilizing 
just hv-EC, that can/could be practical for qual¬ 
ity control or screening purposes. 

EXPERIMENTAL PROCEDURES 
Reagents, Chemicals, and Explosives Standards 

Figure 1 illustrates some of the explosives 
studied here via HPLC-hv-EC and hv-EC ap¬ 
proaches. Standards of these compounds were ob¬ 


tained from the Bureau of Alcohol, Tobacco, and 
Firearms (U.S. Treasury Department) Forensic 
Laboratory, Rockville, Maryland, via the assis¬ 
tance and cooperation of Mr. A. Cantu. Some of 
these explosives were obtained from the FBI 
Academy, Forensic Research and Training Cen¬ 
ter, Quantico, Virginia, via the assistance of Dr. 
T. Rudolph. Two samples of post-blast debris ex¬ 
tracts were also obtained from the above ATF lab¬ 
oratory, with the cooperation of Mr. Rick Strobel. 
Such samples were received as acetonitrile solu¬ 
tions, and were analyzed by direct injection onto 
HPLC-hv-EC, as below. These particular sam¬ 
ples had been analyzed at the ATF by thin-layer 
chromatographic methods and were found to con¬ 
tain NG. A nitroglycerin standard was a sample of 
Parke-Davis Nitrostat-IV, lot AK725, 8mg/ml in¬ 
fusion solution, available as a prescription drug 
for heart ailments. Other organic nitro standards 
were obtained from commercial sources, such 
as: Aldrich Chemical Co. (Milwaukee, Wise.), 
Pfaltz & Bauer Co. (Stanford, Conn.), or Fisher 
Scientific Co. (Medford, Mass.). Inorganic salts 
were obtained from a variety of commercial 



V°2 

H 2?' N "'? H 2 

^N0 2 

RDX 





CHgONOg 

O^CHg—C—CH 2 0N0 2 

ch 2 ono 2 

PETN 

Figure 1. Structures of some 
plosives. 



no 2 

TNC 


NOc 
I d 

h^ N 'ch 2 
O z N-y P- N0 2 
H 2 C "n" CH 2 
no 2 

HMX 

h 2 c—ono 2 
h 2 c—ono 2 

EGDN 

H„C —0N0 9 

2 | 2 

HC—ONOo 

I 

HgC —0N0 2 
NITROGLYCERIN 

the more commonly used ex- 


13 


sources, including: J. T. Baker Chemical Co. 
(Phillipsburg, N.J.), Fisher Scientific Co., Aldrich 
Chemical Co., and others. The HPLC Solvents, 
especially water (HOH) and methanol (MeOH), 
were obtained from Waters Assocs., Inc. (Mil¬ 
ford, Mass.) or MCB Chemicals Co. (Cincinnati, 
Ohio), the latter as their Omnisolv brand of 
HPLC grade solvents. 

Instrumentation and Equipment 

Figure 2 illustrates the overall HPLC-hv-EC in¬ 
strumentation used in all of these studies, and the 
orientation/arrangement of the various parts of 
the analytical system. The HPLC portion in Fig¬ 
ure 2 utilized a Rheodyne Model 7125 syringe 
loading injection valve (Rheodyne Corp., Cotati, 
Calif.), a Laboratory Data Control (LDC) Con- 
stametric II solvent delivery system (Laboratory 
Data Control, Riviera Beach, Fla.), a LiChroma- 
Damp II pluse dampener (Alltech Assocs., Inc., 
Deerfield, Ill.), a Bioanalytical Systems pulse 
dampening column (Bioanalytical Systems, Inc., 
West Lafayette, Ind.), a Photronix Model 816 
HPLC batch irradiator (Photronix Corp., Med¬ 
way, Mass.), a BAS Model LC-4A single elec¬ 
trode amperometric controller or a BAS Model 
LC-4B dual electrode amperometric system for 
HPLC/LCEC, a BAS glassy carbon single or dual 
working electrode with a Ag/AgCl reference elec¬ 
trode, and finally, a Linear Instruments Model 
585 dual pen strip chart recorder (Linear Instru¬ 
ments, Inc., Reno, Nevada). All HPLC injections 
were made with a 25ul flat-tipped Hamilton 
HPLC syringe (Hamilton Corp., Reno, Nevada). 
HPLC mobile phases were de-gassed and filtered 
prior to use via a 0.45um solvent filtration kit 
(Millipore Corp., Bedford, Mass.). Samples for 
HPLC injection were initially filtered with a sam¬ 


ple filtration kit using a 0.45um filter (Millipore 
Corp.). The irradiation finger, Figure 2, was 
maintained at a constant temperature of about 
0-5 °C, with a constant temperature water bath 
(Forma Scientific, Model 2095, VWR Scientific 
Co., Boston, Mass.). Irradiation of the HPLC 
eluents took place inside a 10-12', 1/16" o.d., 
0.030" i.d., Teflon FEP tubing, catalog no. 
HGC-024 (Rainin Instruments Co., Woburn, 
Mass.). Swagelok stainless steel fittings and fer¬ 
rules were used for all of the HPLC-hv-EC con¬ 
nections, except wherein the EC detector cells re¬ 
quired their own, already present connection fit¬ 
tings (Cambridge Valve & Fittings Co., Billerica, 
Mass.). The dual electrode HPLC-hv-EC unit 
utilized HPLC-hv-EC equipment/instrumenta¬ 
tion similar to that described above for the single 
electrode unit, replacing the single electrode am¬ 
perometric controller with the dual electrode/con¬ 
troller system from BAS. In the reductive mode of 
detection, the HPLC mobile phase was first 
de-gassed under nitrogen using an approach al¬ 
ready described elsewhere [Bratin et al. (1981), 
Krull et al. (1983a), Krull et al. (1983b)]. The use 
of a Teflon irradiation line before the EC detector 
in the reductive mode of LCEC did not preclude 
the ability to perform trace explosives analyses at 
moderate working potentials, as below. The 
HPLC columns utilized in these studies were ob¬ 
tained from a variety of sources, including: 1) 
Biophase C i8 , lOum, 25-cm x 4.6-mm i.d. (Bio¬ 
analytical Systems, Inc.); 2) A Perkin-Elmer 
Fast-LC Cig, 3um, 10-cm x 4.6-mm i.d. (Per¬ 
kin-Elmer Corp., Norwalk, Conn.); 3) a Waters 
uBondapak C !8 , lOum, 25-cm x 4.6-mm i.d. (Wa¬ 
ters Associates); and 4) various in-house slurry 
packed C 8 or C !8 reversed phase columns. 


QUARTZ 

TUBE 



stainless steel tubing 


Figure 2. Schematic diagram of an on-line approach for performing nitro compound and explosives analysis via reversed phase 
HPLC with photohydrolytic derivatization after the analytical column via UV lamp irradiation of analytes, followed by oxida¬ 
tive/oxidative EC detection of nitrite generated in photolysis step of overall HPLC-hv-EC analysis. 


14 
























Methods and System Optimization 

The cyclic voltammograms (CV) were obtained 
on a Bioanalytical Systems Model CV-1B unit, us¬ 
ing a supporting electrolyte of 50/50 MeOH/0.1M 
NaCl, with a scan rate of 150mV/sec, with a 
Ag/AgCl reference elctrode and a glassy carbon 
working electrode. The CVs were obtained by 
plotting applied working potentials vs current gen¬ 
erated/observed, in the conventional, standard 
approach. 

The final hv-EC and HPLC-hv-EC systems 
had to be optimized before their use with either 
standard mixtures of explosives or real world sam¬ 
ples, and this was crucial for the photochemical ir¬ 
radiator/reactor part of the overall system, Figure 
2. This was accomplished by varying both the in¬ 
ternal diameter of the Teflon tubing and its total 
length wrapped around the irradiator finger. By 
measuring EC peak heights or current generated 
as a function of either the i.d. or total length, for 
the same concentration of explosives injected with 
hv-EC methods, it was then possible to determine 
the optimum tubing parameters that would pro¬ 
vide maximum nitrite generation with minimum 
nitrite destruction from the various explosives of 
interest here. An external standard of nitrite was 
used, with the lamp off, as a control to determine 
optimization of nitrite generated from the explo¬ 
sives with the lamp on in the hv-EC approaches. 
The optimal flow rate was then determined also 
via flow injection methods (hv-EC), without the 
HPLC column on-line, again using the maximum 
nitrite generated from various nitro compounds or 
explosives. This suggested ideal flow rates and res¬ 
idence times for the final HPLC-hv-EC system. 
The hv-EC system also had to be optimized with 
regard to salt concentration and which salts were 
compatible with both photolysis and EC detector 
conditions. A number of conventional inorganic 
salts were studied in these regards, but only NaCl 
appeared to be totally inert to the photolysis and 
EC conditions, and to be free of impurities that 
might interfere in the final hv-EC analyses. The 
effect of pH also had to be optimized for hv-EC 
approaches, and again this was accomplished by 
using maximum nitrite generated from the same 
standards (nitro compounds) to indicate ideal pH 
values that could then be used in the final 
HPLC-hv-EC studies. All of the final operating 
parameters, as below and in various Figures that 
follow, were then utilized for both the flow injec¬ 
tion studies (hv-EC) and the HPLC-hv-EC anal¬ 
yses of various standard mixtures of explosives 
and real world, post-blast extract samples. 


RESULTS AND DISCUSSION 

Initial Cyclic Voltammogram Studies for Inorgan¬ 
ic Anions, Possible Interferents in hv-EC and 
HPLC-hv-EC for Trace Analysis of Explosives 
and Nitro Compounds 

These HPLC-hv-EC or flow injection analysis 
via hv-EC methods depend initially on the photo- 
lytic or photohydrolytic generation of an inorgan¬ 
ic or organic anion from an appropriate organic 
precursor for trace organic analysis. These needs 
are quite similar to those needed in photoconduc¬ 
tivity detection in HPLC trace organic analysis. It 
is also possible that certain inorganic anions, elec- 
trochemically active in the absence of any photol¬ 
ysis, might be converted via photolysis to electro- 
chemically active species/ions. Thus, these basic 
approaches may yet prove applicable for both or¬ 
ganic and inorganic trace analyses, in addition to 
the applications described herein. In FIA (hv-EC) 
approaches, there may often be a problem of in¬ 
terferences arising in the direct analysis of an ex¬ 
plosive compound or organic nitro material, by 
one or more inorganic/organic anions already pre¬ 
sent in the same sample matrix/solution. In order 
to determine such possible interferents, we ob¬ 
tained a series of cyclic voltammograms (CV) for 
four typical inorganic anions of interest as possi¬ 
ble interferents or photolysis products derived 
from suitable organic precursors, Figure 3. Of the 
four inorganic anions of most interest for final 
HPLC-hv-EC applications, it is quite clear that 
nitrate (N0 3 ~) is not oxidized at the potentials of 
interest in EC detection. At the same time, Figure 
3 indicates that nitrite (NCK), iodide (I-), and 
bromide (Br-) all have very different optimal oxi¬ 
dation potentials for maximum current generated 
in either CV or EC detection. Hence, it should be 
readily possible to differentiate between an or¬ 
ganic nitrate ester, an aromatic C-nitro derivative, 
an organic alkyl nitrite (R-O-NO), an organoio- 
dine (R-I) compound, an organobromine (R-Br) 
substance, each of these leading to the corre¬ 
sponding anions via photolytic derivatization (i.e., 
N0 3 _ /N0 2 “ , NOf , NO/NCK , I , or Br ). How¬ 
ever, an organic nitrate ester (R-0-N0 2 ) could 
conceivably lead to both nitrite and nitrate on irra¬ 
diation, while an aromatic nitro compound or an 
alkyl C-nitro material might only lead to inorgan¬ 
ic nitrite on irradiation. It is also possible that the 
initially formed nitrate or nitrite species could fur¬ 
ther react with oxygen in the aqueous based solu¬ 
tion or HPLC mobile phase, leading to fur¬ 
ther/additional EC active species. It is also possi- 


15 


d 






Figure 3. Cyclic voltammograms of various inorganic anions of interest in HPLC-hv-EC trace analysis for organic precursors 
leading to such anions by photolysis: a) supporting electrolyte of MeOH/0. 1 M NaCl (50/50, v/v); b) 0.0065M KNO 3 ; c) 0.0048M 
NaN0 2 ; d) 0.0026M KI; and e) 0.0035M KBr. All CVs performed at a glassy carbon electrode with scan rate of 150mV/sec, x-axis 
volts vs Ag/AgCi, y-axis in microamperes. 


ble that other electroactive species, in addition to 
nitrate/nitrite, could be formed from certain or¬ 
ganic nitro compounds on initial photolysis/irra¬ 
diation. Our results support the already estab¬ 
lished fact that photolysis of organic nitrate esters 
and aromatic C-nitro compounds can lead to re¬ 
lease of inorganic nitrite, and that this is then 
readily detected via oxidative EC methods 
[Binkley and Koholic (1979)]. Since inorganic ni¬ 
trite was of most interest here as the major photol¬ 
ysis product derived from all of the explosives and 
nitrate esters studied here, we obtained a separate 
linear hydrodynamic voltammogram using flow 
injection analysis methods. This plot indicated 
usable oxidative working potentials for EC detec¬ 
tion of nitrite of about 4-0.8 to +1.0V. Indeed, 
such working potentials for the analysis of nitrite 
had already been suggested in the existing litera¬ 
ture [Sherwood and Johnson (1981), Davenport 
and Johnson (1974)]. Thus, for most of the studies 
that follow, especially in the HPLC-hv-EC work, 
we have tended to emphasize oxidative potentials 
around 4- 1.0V, with either a glassy carbon single 
or dual working electrode system. 


In order to further delineate which inorgan¬ 
ic/organic anions might cause interferences in the 
hv-EC or HPLC-hv-EC analyses of explosives 
and organic nitro compounds, we determined the 
EC oxidative responses for a large number of such 
anions with and without the lamp/irradiator 
turned on, Table 1. These overall results suggest 
that there are relatively few inorganic or organic 
anions that produce the same qualitative results as 
does inorganic nitrite under these particular EC 
operating potentials/conditions. When quantita¬ 
tive values are obtained for the oxidative re¬ 
sponses for nitrite at two different working poten¬ 
tials, and these are then compared with the same 
values for other anions that might be interferents 
in the analysis for nitrite, it is readily seen that on¬ 
ly nitrite has a characteristic ratio of EC re¬ 
sponses. Thus, the use of dual detector response 
ratioing in hv-EC or HPLC-hv-EC could/should 
provide almost unequivocal qualitative and quan¬ 
titative fingerprints or handles for individual inor¬ 
ganic anions generated via photolysis from very 
specific organic precursors. Indeed, these initial 
speculations have now been confirmed, as below. 


Table 1. SUMMARY OF POSSIBLE INORGANIC ANION RESPONSES IN HPLC-hv-EC USING hv-EC 
Anion Studied EC Active With Lamp Off EC Active With Lamp On 



40.8 V 

+ 1.0V 

+ 0.8 V 

+ 1.0 V 

ci- 

NO 

NO 

NO 

NO 

C 103 - 

NO 

NO 

NO 

NO 

C 104 - 

NO 

NO 

NO 

NO 

Br- 

NO 

NO 

NO 

NO 

F- 

NO 

NO 

NO 

NO 

I- 

YES 

YES 

YES 

YES 

IO 3 - 

NO 

NO 

YES 

YES 

I 0 4 - 

NO 

NO 

YES 

YES 

CO 3-2 

YES 

YES 

YES 

YES 

HCO 3 - 

NO 

NO 

YES 

YES 

no 2 - 

YES 

YES 

YES 

YES 

NO 3 - 

NO 

NO 

YES 

YES 


16 














Table 1. SUMMARY OF POSSIBLE INORGANIC ANION RESPONSES IN HPLC-hv-EC USING hv-EC—Cont. 


Anion Studied 

EC Active W ith Lamp Off 

F.C Active W ith Lamp On 


+ 0.8 V 

+ 1.0 V 

+ 0.8 V 

+ 1.0 v 

SO 3-2 

YES 

YES 

NO 

NO 

SO 4- 2 

NO 

NO 

NO 

NO 

HSO 3 - 

YES 

YES 

YES 

YES 

S -2 

YES 

YES 

YES 

YES 

BENZOATE 

NO 

NO 

YES 

YES 

ACETATE 

NO 

NO 

NO 

NO 

CNS- 

NO 

YES 

YES 

YES 

CN- 

YES 

YES 

YES 

NO 

h 2 po 4 - 

NO 

NO 

YES 

YES 

hpo 4 - 

NO 

NO 

YES 

YES 

hpo 2 - 

NO 

NO 

NO 

NO 

Cr0 4 -2 

NO 

NO 

NO 

YES 

Cr 2 0 7 -2 

NO 

NO 

NO 

YES 

H 2 As0 4 - 

NO 

NO 

NO 

NO 


a. These analyses of possible anion responses via dual electrode EC in hv-EC approaches were done using flow injection methods, 
with no HPLC column yet in-line. Dual electrode glassy carbon cell used here. 


Qualitative EC Oxidative Responses for Explo¬ 
sives, Drugs, Aromatic Nitro Compounds, and 
Organic Nitrate Esters via Photolysis-EC (FIA) 
Methods 

Knowing the optimum potentials for oxidative 
EC detection of the expected anions to be derived 
from explosives or other nitro compounds via 
hv-EC methods, it was then necessary to demon¬ 
strate that such analytes would indeed respond in 
flow injection analysis (FIA) under these irradia¬ 
tion conditions. At the same time, it was necessary 
to show that there would be no response on the EC 
detector for such compounds/substrates with the 
lamp off, Table 2. These studies were done after 
the hv-EC system had been optimized, as already 
described (Experimental Procedures). Of interest 


here is the clear observation that inorganic nitrate 
does not show any response at these oxidative po¬ 
tentials with the lamp off, as expected, but that af¬ 
ter irradiation, it does show a very good EC re¬ 
sponse at these same working potentials. This sug¬ 
gests that there may be some photoreduction of 
the nitrate to nitrite occurring, and that it is the 
final nitrite that is being detected in hv-EC or 
HPLC-hv-EC with the lamp turned on. It would 
appear, therefore, that FIA using hv-EC methods 
might provide a rapid, reliable, specific, sensitive, 
and quite reproducible method of direct analysis 
for these and other explosives and related organic 
nitro compounds. This would include nitro deriva¬ 
tives of various polycyclic aromatic hydrocarbons 
(PAHs), such as 9-nitroanthracene, Table 2. Such 


Table 2. DUAL ELECTRODE EC RESPONSES FOR VARIOUS EXPLOSIVES, NITRATE ESTERS, AROMATIC NITRO 
COMPOUNDS, DRUGS, AND RELATED COMPOUNDS VIA PHOTOLYSIS-ELECTROCHEMICAL 


DETECTION (hv-EC). 
Explosive or Nilro 

Compound EC Active 

Compound FC Active 

Compound 

+ 0.8V 

With Lamp Off 

+ 1.0V 

+ 0.8V 

With Lamp On 

+ 1.0V 

TNT 

NO 

NO 

YES 

YES 

RDX 

NO 

NO 

YES 

YES 

TETRYL 

NO 

NO 

YES 

YES 

NG 

NO 

NO 

YES 

YES 

ISDN 

NO 

NO 

YES 

YES 

/so-PROPYLNITRATE 

NO 

NO 

YES 

YES 

/j-PROPYLNITRATE 

NO 

NO 

YES 

YES 

9-NITROANTHRACENE 

NO 

NO 

YES 

YES 

o-NITROTOLUENE 

NO 

NO 

YES 

YES 

DINITROBENZENE 

NO 

NO 

YES 

YES 

DINITROTOLUENE 

NO 

NO 

YES 

YES 

SODIUM NITRATE 

NO 

NO 

YES 

YES 

SODIUM NITRITE 

YES 

YES 

YES 

YES 


a. These determinations were performed via flow injection methods, with no HPLC column on-line, using just the basic photoly- 
sis-EC system (hv-EC). 


17 





compounds are of current widespread interest and 
concern as possible environmental pollutants hav¬ 
ing demonstrated animal/human carcinogenic 
and/or mutagenic properties and potentials. How¬ 
ever, the use of FIA techniques for such analyses 
might only be feasible wherein the sample matrix 
is relatively simple, and/or wherein there would be 
very few, if any anionic interferents already pre¬ 
sent in the sample matrix that could produce simi¬ 
lar dual electrode responses at these particular 
operating/working potentials used for organic ni- 
tro derivatives. 

We have, in a separate, but related study, inves¬ 
tigated the dual electrode response ratios at fixed 
concentrations injected for two different oxidative 
potentials, using various explosives and nitro de¬ 
rivatives, Table 3. These results were also obtained 
using flow injection methods, hv-EC, wherein the 
same concentrations of each analyte were injected 
under identical working/operating conditions. 
These overall results suggest that each and every 
individual explosive, drug, nitroaromatic, or ni- 
tro-PAH, may have its own unique dual detector 
response ratio. Such a quantitative characteristic 
for each analyte could then be used to further con¬ 
firm its presence in a simple sample matrix via 
hv-EC (FIA) methods, or in more complex sample 
matrices, using HPLC-hv-EC approches. That is, 
wherein an explosive is thought to be present in a 
real-world, post-blast extract sample, its presence 
could be more accurately confirmed using the dual 
detector response ratio for the analyte in the sam¬ 
ple, and comparing this value with the corre¬ 
sponding value obtained for an authentic standard 
of the suspected explosive. This method has in¬ 
deed now been applied to an actual, real-world ex¬ 
plosion debris extract, as indicated below. 

Table 3. DUAL ELECTRODE RESPONSE RATIOS AT 
FIXED CONCENTRATIONS INJECTED FOR 
TWO DIFFERENT OXIDATIVE POTENTIALS, 
+ 1.0V/ + 0.8V, FOR VARIOUS EXPLOSIVES 
AND NITRO DERIVATIVES. 2 
Compound Studied Dual Electrode Response Ratios 
NG 4.33 

TETRYL 2.00 

TNT 2.25 

RDX 3.00 

ISDN 1.64 

a. These detector response ratios were determined via flow in¬ 
jection analysis, hv-EC, at the two working potentials of 
+ 1,0V and 4- 0.8V. Ratios were calculated at the same con¬ 
centration of each nitro derivative injected for plots of the 
detector responses at a number of concentrations injected 
at these two working electrode potentials. All hv-EC analy¬ 
ses were performed within the same working day. 


Calibration Plots via hv-EC and Minimum Detec¬ 
tion Limits for Various Explosives via HPLC- 
hv-EC Approaches/Methods 

We have now obtained, via single and dual elec¬ 
trode EC methods, in hv-EC (FIA), a number of 
calibration plots and minimum detection limits for 
various explosives, aromatic nitro compounds, 
and organic nitrate esters, including: w-propylni- 
trate, /so-propylnitrate, 9-nitroanthracene, inor¬ 
ganic nitrite, RDX, NG, TETRYL, and isosorbide 
dinitrate (ISDN). In the hv-EC single electrode 
work, an oxidative working potential of + 1.0V 
was used, while in the dual electrode hv-EC 
studies, working potentials of + 1.0V and -l-0.8V 
were utilized. These dual electrode calibration 
plots at two different working potentials then pro¬ 
vided us with the detector response ratios indi¬ 
cated above, Table 3. Figure 4 indicates the cali¬ 
bration plot obtained for inorganic nitrite, with a 
correlation coefficient of 0.9993 and a minimum 
detection limit (MDL) of about 0.8ng/20ul injec¬ 
tion (40ppb). Figure 5 is a similar calibration plot 
for the explosive or coronary vasodilator nitrogly¬ 
cerin (NG), again with a coefficient of linearity in 
excess of 0.999. Calibration plots for RDX, 
TETRYL, and TNT are indicated separately in 
Figure 6, together with each correlation coeffi¬ 
cient and MDL. These other minimum detection 
limits indicated in these calibration plots have now 
been improved further in the HPLC-hv-EC re¬ 
sults described below. Figure 7 illustrates the cali¬ 
bration plots for two simple aliphatic nitrate es¬ 
ters, /7-propylnitrate and Ao-propylnitrate, with 
the amounts injected as indicated and observed 
EC peak heights, at a working potential of 
+ 1.0V. Figure 8 is a similar plot of linearity for 
the coronary vasodilator isosorbide dinitrate, with 
a correlation coefficient of 0.9998 and a MDL of 
about 12.5ng/20ul injection. One last calibration 
plot using single electrode hv-EC methods is pre¬ 
sented in Figure 9, for an aromatic nitro deriva¬ 
tive, 9-nitroanthracene, with a correlation coeffi¬ 
cient of 0.9996 and a MDL of about 1.6ng/20ul 
injection. In all of these calibration plots, we have 
emphasized amounts injected ranging from the 
low ng/injection to several hundred ng/injection, 
or approximately two orders of magnitude in 
amounts studied. However, it should be empha¬ 
sized here that the actual calibration plot linear¬ 
ities could/would exceed the upper amounts in¬ 
jected, but that we have been most interested in 
amounts involved in trace explosives work/anal¬ 
yses. 


18 




Figure 4. Calibration plot of sodium nitrite (NaN02) in flow 
injection analysis with hv-EC using glassy carbon electrode in 
EC at + 1.0V. 



Figure 5. Calibration plot for nitroglycerin using flow injec¬ 
tion analysis with photolysis-electrochemical detection via sin¬ 
gle electrode at 1.0V. 



Figure 6. Calibration plots for RDX, TETRYL, and TNT 
using flow injection analysis with hv-EC using glassy carbon 
working electrode at + 1.0V. 




Figure 7. Calibration plots for two aliphatic nitrate esters, 
fl-propylnitrate and /'so-propylnitrate, using flow injection 
analysis with photolysis-electrochemical detection via single 
electrode at -I- 1,0V. 


19 











Figure 8. Calibration plot of isosorbide dinitrate in flow injec¬ 
tion analysis with hv-EC using glassy carbon electrode at 
+ 1.0V. 



NANOGRAMS 9-NITRO ANTHRACENE INJECTEO 


Figure 9. Calibration plot of 9-nitroanthracene in flow injec¬ 
tion analysis with hv-EC using glassy carbon electrode at 
+ 1.0V. 


A number of similar calibration plots using dual 
electrode detection in hv-EC are also presented 
here, in order to emphasize the magnitude of the 
differences possible in the ratios of dual detector 
responses for quite related analytes/compounds. 
Thus, Figure 10 illustrates a typical set of dual de¬ 
tector responses, at the working potentials indi¬ 
cated, for isosorbide dinitrate. This type of dual 
detector study then provided the response ratios 
already indicated above, Table 3. Figures 11-14 
are the related dual detector calibration plots now 
obtained for four separate explosive compounds, 
viz., RDX (Figure 11), nitroglycerin (Figure 12), 
TNT (Figure 13), and TETRYL (Figure 14). In all 
of these studies, the dual detector electrodes were 
operated at + 1.0V and + 0.8V in the parallel 
mode of operation, with concentrations of each 
compound injected ranging from the low ppm to 
about 10 ppm levels. However, again it must be 
emphasized that linearities of dual detector re¬ 
sponses for these and other nitro derivatives 
should exceed the upper ranges indicated here, but 
that we have not yet demonstrated this experi¬ 
mentally. In any event, such dual detector re- 



ISO-SORBIDE DINITRATE CONCENTRATION (PPM) 

Figure 10. Plot of dual electrode EC responses, peak heights 
vs. concentrations of isosorbide dinitrate injected (ppm), at 
two different oxidative potentials, using flow injection analysis 
with hv-EC with EC cell in parallel orientation. Glassy carbon 
electrode used in EC cell. 


20 










Figure 11. Plot of dual electrode EC responses, peak heights vs 
concentrations of RDX injected (ppm), at two different oxida¬ 
tive potentials, using flow injection analysis with hv-EC with 
EC cell in parallel orientation. 

sponses are linear over at least 1-2 orders of 
magnitude, ranging from less than 100 ppb to at 
least 10 ppm. 

With regard to minimum detection limits 
(MDL) for the explosives of interest here, these 
are summarized in Table 4, with the experimental 
conditions as indicated therein. These determina¬ 
tions of MDLs were made using injection volumes 
of 20ul, but wherein larger injection volumes have 
been now used, i.e., 100-200ul, such final MDLs 
have been reduced by a factor of 5-10 fold. Thus, 
for explosives such as RDX, TETRYL, and TNT, 
we have realized overall MDLs via HPLC-hv-EC 
methods of about 5ppb, which would appear ideal 
for trace analyses. It is also possible that overall 
MDLs could be further improved by reducing the 
total dead volume now present in the instrumental 
system, so that peak shapes and peak heights (used 
for MDL studies) would be further improved/op¬ 
timized. All of the minimum detection limits re¬ 
ported here were determined using peak height 
measurements with a final signal/noise ratio of at 
least 3/1 overall. 



(NITROGLYCERIN, NG) 

Figure 12. Plot of dual electrode EC responses, peak heights vs 
concentrations of nitroglycerin injected (ppm), at two different 
oxidative potentials, using flow injection analysis with hv-EC 
with EC cell in parallel set-up. 

Table 4. MINIMUM DETECTION LIMITS FOR EXPLO¬ 
SIVES AND DRUGS VIA HPLC-hv-EC* 


Compound Name 

Minimum 

i Detection Limit (MDL) b 

RDX 

500 pg = 

25 ppb 

TETRYL 

500 pg = 

25 ppb 

TNT 

500 pg = 

25 ppb 

NG 

4.0 ng = 

200 ppb (0.200 ppm) 

ISDN 

2.5 ng = 

125 ppb (0.125 ppm) 

NaNQ 2 

1.56 ng = 

= 78 ppb 


a. HPLC-hv-EC conditions used a C-18 RP column, 3um, 
10-cm x 4.6-mm i.d., with mobile phase of 50/50 
MeOH/0.1M MaCI, 0.6 ml/min flow rate, + 0.8V oxida¬ 
tive EC detection. 

b. Injections were made in 20ul volumes, MDL given in terms 
of mass of analyte injected and concentration, ppb = 
parts-per-billion; ppm = parts-per-million, etc. 

Single Electrode EC Detection via HPLC-hv-EC 
for Explosives and Drugs 

We have now utilized both single and dual elec¬ 
trode detection for various explosives mixtures, 
but because the dual approach provides more 
qualitative and quantitative information on a sin¬ 
gle injection, these have been emphasized 


21 


















Figure 13. Plot of dual electrode EC responses, peak heights vs 
concentrations of TNT injected (ppm), at two different oxida¬ 
tive potentials, using flow injection analysis with hv-EC with 
EC cell in parallel orientation. 



Figure 14. Plot of dual electrode EC responses, peak heights vs 
concentrations of TETRYL injected (ppm), at two different 
oxidative potentials, using flow injection analysis with hv-EC 
with EC cell in parallel orientation. 


throughout. Figure 15 illustrates a typical single 
electrode chromatogram (A) for three standard 
explosives, viz., RDX, TETRYL, and TNT, with 
the irradiation lamp turned on and the detector at 
+ 1.0V working potential. Figure 15B is the same 
HPLC-hv-EC analysis of these same three explo¬ 
sives, but now with just the lamp turned off, all 
other operating parameters identical to those in 
Figure 15A. Finally, Figure 15C indicates the sin¬ 
gle electrode response for a mixture of NG and 
ISDN, with specific analytical parameters as indi¬ 
cated. Mannitol is present in Figure 15C because it 
was present in the sample of ISDN utilized in these 
studies, but since it is chromatographically re¬ 
solved from the ISDN and NG, it does not present 
any analytical problems. Clearly, as Figures 15A 
and 15B so clearly demonstrate, detection of these 
and other explosives/drugs/nitro compounds, is 
entirely dependent on the irradiation step, 
on-line, post-column, for the generation of the 
EC detectible species (nitrite, etc.). Although the 
+ 1.0V working potential used here was optimal 
for these particular analytes, it is clear that a vari¬ 


ety of other oxidative and perhaps reductive work¬ 
ing potentials could also be used in this 
HPLC-hv-EC work. That is, inorganic nitrite, as 
an irradiation product of various explosives, can 
be detected oxidatively, but others have already 
shown that underivatized explosives can also be 
detected in the reductive EC mode of operation 
[Bratin et al. (1981)]. Hence, it should be possible 
to utilize both oxidative and reductive dual elec¬ 
trode detection for these explosives, with and 
without the irradiation lamp turned on in 
HPLC-hv-EC approaches. Thus, with the lamp 
off, only reductive EC detection would/should be 
possible, but with the irradiator on, oxidative EC 
should detect nitrite and reductive EC would de¬ 
tect intact explosives or nitro compounds. Thus, 
although single electrode detection is useful and 
practical for real world samples, dual electrode de¬ 
tection in LCEC or HPLC-hv-EC or hv-EC can 
provide significant qualitative and quantitative 
advantages, as indicated/summarized below. 


22 















10 nA 



LAMP ON 


LAMP OFF 



LAMP ON 


Figure 15. HPLC-hv-EC single electrode chromatograms for three explosives: RDX, TNT, and TETRYL. standards, using RP 
C-8 reversed phase column, lOum, 25-cm x 4.6-mm i.d., with 50/50 MeOH/O.lM NaCl mobile phase at 1.4 ml/min, glassy carbon 
electrode operated at + 1,0V oxidatively. (A) hv lamp turned on; (B) hv lamp turned off; (C) hv lamp on with NG and ISDN stand¬ 
ards injected. 


Dual Electrode Detection in HPLC-hv-EC for 
Explosives and Drugs 

Figure 16 illustrates a typical dual electrode, 
oxidative/oxidative parallel HPLC-hv-EC set of 
chromatograms for a mixture of three standard 
explosives, RDX, TETRYL, and TNT, with con¬ 
ditions as indicated. Detection here used EC meth¬ 
ods in the parallel mode, with a glassy carbon 
working electrode operated at + 1.0V and + 0.8V. 
Once again, alternative oxidative/oxidative, oxi¬ 
dative/reductive, and/or reductive/reductive po¬ 
tentials are possible and practical here, as above 


with the single working electrode situation. The 
next set of dual electrode HPLC-hv-EC chroma¬ 
tograms, Figure 17, is almost identical in operat¬ 
ing conditions and amounts of explosives injected 
to those used to derive Figure 16 chromatograms. 
The only difference is that one of the two dual 
electrodes in Figure 17 is operated at + 0.90V, 
rather than the + 0.80V used for this second elec¬ 
trode in Figure 16. The other working electrode in 
both Figures 16 and 17 has been maintained at 
+ 1.0V throughout. The responses thus observed 
at the + 1.0V electrode in both Figures are about 


23 




















EC DETECTOR RESPONSE 
(OXIDATIVE MODE, +I.OV AT W g ) 


TIME (MIN) 

0 4 8 12 16 

I_I_I_I_I 



EC DETECTOR RESPONSE 
(OXIDATIVE MODE, +I.OV AT \^> 

TIME (MIN) 

0 4 8 12 16 

I_I_I_I-1 



PARALLEL 





GC 

_i 

>- 

oc 


>- 

oc 

t- 

LU h- 



EC DETECTOR RESPONSE 
(OXIDATIVE MODE, ♦ 0.80V AT W,) 


LU Z 


X H- 

Q 



EC DETECTOR RESPONSE 
(OXIDATIVE MODE, + 0.90 V AT W,) 


Figure 16. HPLC-hv-EC dual electrode chromatograms of 
three explosives, TDX, TETRYL, and TNT, using C-18 RP, 
3um, 10-cm x 4.6-mm i.d. column with 50/50 MeOH/O.lM 
NaCl at 0.6 ml/min flow rate. Dual electrodes operated in oxi¬ 
dative/oxidative modes. 


Figure 17. HPLC-hv-EC dual electrode chromatograms of 
three explosives, RDX, TETRYL, and TNT, using C-18 RP, 
3um, 10-cm x 4.6-mm i.d. column, with 50/50 MeOH/O.lM 
NaCl at 0.6 ml/min flow rate. Dual electrodes operated in oxi¬ 
dative/oxidative modes, glassy carbon surfaces. 


the same in peak heights, but the responses at the 
+ 0.90V electrode in Figure 17 are much great¬ 
er/larger than those at the + 0.80V electrode in 
Figure 16, as expected from the linear hydrody¬ 


namic voltammogram obtained initially for nitrite 
ion. 

Figure 18 illustrates another set of dual elec¬ 
trode HPLC-hv-EC chromatograms, herein util- 


24 


























EC DETECTOR RESPONSE 
(REDUCTIVE MODE, -0.55 V AT ) 

TIME (MIN) 



PARALLEL 


• W 2 


GC 


x 

Q _J 

ce x 



EC DETECTOR RESPONSE 
(OXIDATIVE MODE, + I.OV AT W,) 


Figure 18. HPLC-hv-EC dual electrode chromatograms for 
the three explosives, RDX, TETRYL, and TNT, using C-18, 
RP column, 3um, 10cm x 4.6-mm i.d., 50/50 MeOH/O.lM 
NaCl mobile phase at 0.6 ml/min flow rates. Glassy carbon 
dual electrodes operated in oxidative/reductive modes. 

izing oxidative/reductive approaches, with one 
working electrode held at - 0.55V and the other at 
+ 1.00V, for the three explosives of interest, 
RDX, TETRYL, and TNT. Although the reduc¬ 
tive responses for these three explosives, at the lev¬ 


els injected here, are somewhat poor, at least RDX 
and TETRYL are discernible above the back¬ 
ground noise level. We believe that the responses 
observed here and elsewhere for these nitro com¬ 
pounds at the reductive potential of -0.55V are 
arising from electrochemical reduction of the 
starting, intact analyte, underivatized, with the ni¬ 
tro groups still intact despite having gone through 
the irradiator with the lamp on. If all of these ex¬ 
plosives had been fully irradiated to form nitrite 
ions, and none of the original compounds re¬ 
mained, then there would not be any response at 
the reductive working electrode. Wherein these 
same studies are performed with the lamp turned 
off, only the reductive chromatogram in Figure 18 
remains, at somewhat greater peak heights for 
each explosive, since now none is being de- 
stroyed/photolyzed with the lamp off. Similarly, 
Figure 19 illustrates the same type of dual detector 
responses in HPLC-hv-EC, oxidative/reductive, 
for the two drugs ISDN and NG, with the specific 
operating conditions as indicated. The other peak 
in Figure 19 is due to mannitol, which happens to 
be present in the particular sample of ISDN util¬ 
ized/available for these studies. Again, in both 
oxidative and reductive EC operating modes, each 
of these two nitrate esters, NG and ISDN, provide 
significant responses under HPLC-hv-EC condi¬ 
tions. We believe that in this situation, the oxida¬ 
tive response is due to nitrite released from the ni¬ 
trate esters, and the reductive response is due to 
nitrate (N0 3 ^ ) released from the same nitrate ester 
precursors. With the lamp turned off here, there 
are no EC responses in either the oxidative or re¬ 
ductive modes. The dual electrode EC analysis for 
ISDN and NG has also been performed in 
HPLC-hv-EC with both working electrodes in the 
oxidative modes, Figure 20. Here, one of the two 
glassy carbon working electrodes is operated at 
+ 1.0V and the other at + 0.9V, with the other 
operating conditions as indicated. The dual detec¬ 
tor response ratios for these two compounds in 
Figure 20 are clearly quite different from the simi¬ 
lar ratios that would be obtained from these same 
compounds in Figure 19. Thus, dual detector re¬ 
sponse ratios can be easily obtained via two sepa¬ 
rate injections of the same analytes with appropri¬ 
ate changes in the operating potentials of the two 
working electrodes. 

Dual Electrode HPLC-hv-EC Detection of Real 
World Explosion Debris Samples 

Figure 21 is a set of HPLC-hv-EC dual elec¬ 
trode chromatograms for a real world sample re- 


25 









EC DETECTOR RESPONSE 
(REDUCTIVE MODE, -0.55V AT 

TIME (MM) 

O 4 8 12 

I_I_I-1 



GC 


Q 

(/) 



EC DETECTOR RESPONSE 
(OXIDATIVE MODE,* 1.0 V AT W,) 

Figure 19. HPLC-hv-EC dual electrode chromatograms for 
the drugs NG and ISDN, using C-18 RP, 3um, column, 10-cm 
x 4.6-mm i.d., 50/50 MeOH/O.lM NaCl mobile phase at 0.6 
ml/min flow rate. Dual electrodes operated in the oxidative/re¬ 
ductive modes, glassy carbon surfaces. 

suiting from a pipe bomb blast under a private 
car, wherein the post-blast debris was first ex¬ 
tracted with acetonitrile. This solution was then 
pre-concentrated, and analyzed first by thin-layer 


EC DETECTOR RESPONSE 
(OXIDATIVE MODE, + 1.0 V AT Wg) 


TIME (MIN) 

0 4 8 12 

I_I_I_I 



Q 


UJ to 
Q — 

CQ 

QL 

O 

CO 

o 

to 


_J — CT 

o z 



EC DETECTOR RESPONSE 
(OXIDATIVE MODE, +0.90V AT W,) 

Figure 20. HPLC-hv-EC dual electrode chromatograms for 
the drugs NG and ISDN using C-18, RP, 3um column, 10-cm 
x 4.6-mm i.d., 50/50 MeOH/O.lM NaCl mobile phase at 0.6 
ml/min flow rate. Dual glassy carbon electrodes operated in 
oxidative/oxidative modes, as indicated. 

chromatography (TLC) within the labs of the 
Bureau of Alcohol, Tobacco, and Firearms (U.S. 
Treasury Department). This TLC analysis indi¬ 
cated the possible presence of NG, and this was 
then verified and confirmed using our 
HPLC-hv-EC approaches. Although this particu¬ 
lar sample contained crankcase oil together with 
the NG, the NG was satisfactorily resolved and 
separated from such other interferents present by 
the HPLC conditions used. The NG could then be 


26 













EC DETECTOR RESPONSE (OXIDATIVE MOOE, +0.8V AT V^> 





TIHI (MIN) 

EC DETECTOR RESPONSE (OXIDATIVE MODE, ♦ 0.9V AT W,) 

Figure 21. HPLC-hv-EC dual electrode chromatograms for a 
real world sample of post-blast debris extracts containing NG 
by TLC analysis. Conditions used a RP, C-18 column, 3um, 
10-cm x 4.6-mm i.d., 50/50 MeOH/O.lM NaCl mobile phase 
at 0.6 ml/min flow rate, glassy carbon dual electrodes operated 
in oxidative/oxidative modes, as indicated. 

clearly identified and determined with the irradia¬ 
tion lamp turned on. Figure 21 (left). Indeed, the 
two chromatograms in Figure 21 were obtained 
first with the lamp on (left) and then with the lamp 
off (right). With the lamp off, only the interfer- 
ents were observed, but no peak is seen at the 
known/determined retention time (t r ) for a stand¬ 
ard of NG. With the lamp turned on, Figure 21 
(left), NG is now clearly evident, at the correct re¬ 
tention time/volume for the standard NG. Thus, 
these results, using dual electrode detection, at the 
working oxidative potentials of + 0.8V and 
+ 0.9V, together with the lamp on/off method, 
strongly confirm the original TLC identification 
of NG being present in this particular real world 
sample of debris extracts. This information is in 
addition to the more customary identification in 
HPLC based on retention times/volumes vs a 
standard injected under identical analytical condi¬ 
tions. Were additional confirmatory evidence nec¬ 
essary, this could readily be obtained by compar¬ 
ing the dual electrode response ratios at various 
working potentials for the suspected NG in this 


sample with the same ratios obtained for authentic 
NG analyzed under the same set of HPLC-hv-EC 
conditions. Indeed, when this was determined for 
this sample, these two set of detector response ra¬ 
tios were identical within experimental error/con¬ 
ditions. Thus, these overall methods of trace ex¬ 
plosives analysis provide a very high, perhaps 
unique, degree of analyte specificity for individual 
explosives present in complex real world samples. 

CONCLUSIONS 

We have now developed, optimized, and ap¬ 
plied a somewhat newer approach for the trace 
analysis of organic nitro compounds and explo¬ 
sives/drugs. These overall HPLC-hv-EC methods 
have been applied to a number of standard explo¬ 
sives and organic nitro compounds, using both 
single and dual electrode detection. Such overall 
methods have also been applied to certain 
real-world, post-blast explosion debris extracts 
suspected of containing NG. We have demon¬ 
strated the dual electrode responses for various ex¬ 
plosives and related nitro compounds, as a func¬ 
tion of the working potentials applied, by plotting 
amounts injected in terms of concentrations (ppm) 
or absolute amounts (ng) vs peak heights/currents 
generated. The overall selectivity of these methods 
far exceeds that already possible via single elec¬ 
trode HPLC-hv-EC methods. It has further been 
shown that these overall approaches for the deter¬ 
mination of nitro compounds can be readily and 
quickly applied to materials such as: explosives, 
drugs and veterinary products, nitrate ester com¬ 
pounds, nitro aromatics, nitro-PAHs, and related 
nitro derivatives, be these O-nitro, C-nitro, or 
N-nitro in nature. Calibration plots and linearities 
of EC response in both single and dual electrode 
methods for various nitro compounds have also 
been determined and described, together with cer¬ 
tain established minimum detection limits using 
these HPLC-hv-EC methods of analysis. It is sug¬ 
gested by these results that hv-EC (FIA) and 
HPLC-hv-EC analytical approches should find 
wide applicability and acceptance in a number of 
areas of trace organic or inorganic analysis. Such 
extensions of the work already completed and de¬ 
scribed here are already in progress in our labora¬ 
tories. 

ACKNOWLEDGEMENTS 

We thank V. Berry for the loan of a Photronix 
water irradiator used in the initial parts of this 
study. Samples of some explosives standards were 


27 



















obtained from T. Rudolph of the FBI Academy’s 
Forensic Research and Training Center, Quantico, 
Virginia. Additional explosives standards were 
provided by A. Cantu of the Bureau of Alcohol, 
Tobacco, and Firearms’ Forensic Laboratory, 
Rockville, Maryland. Samples of post-blast debris 
extracts were provided by R. Strobel of the ATF 
Forensic Laboratory, Rockville, Maryland. The 
sample of isosorbide dinitrate (ISDN) was pro¬ 
vided by L. Gershman of the Boston District Of¬ 
fice of the U.S. Food and Drug Administration, 
Boston, Mass. The dual electrode cells used in this 
study were provided via the assistance of P. 
Kissinger of Boanalytical Systems, Inc. 

Mr. X-D. Ding was a Visiting Scholar from the 
Government of China during the time that these 
studies were undertaken. We are very grateful to 
his Government and to the Chinese Academy of 
Sciences, Beijing, China, for allowing Mr. Ding to 
collaborate in these studies at Northeastern Uni¬ 
versity. 

These studies were supported, in part, by a 
grant from the Analytical Research Department of 
Pfizer, Inc., Groton, Connecticut to Northeastern 
University. Additional funding was provided, in 
part, by a grant from the NIH Biomedical Re¬ 
search Support Grant No. RR07143, Department 
of Health and Human Services, to Northeastern 
University. We are most grateful and appreciative 
of these sources of financial assistance, without 
which this work could not have been undertaken 
or completed. 

This is contribution number 160 from the Insti¬ 
tute of Chemical Analysis at Northeastern Uni¬ 
versity. 

REFERENCES 
Abbreviations used: 

HPLC = high performance liquid chromatog¬ 
raphy; hv = photolysis/photohydrolysis/pho¬ 
tochemical derivation; EC = electrochemical 
detection; UV = ultraviolet detection; HOH = 
water; MeOH = methanol; MDL = minimum 
detection limits; ppm = parts-per-million; ppb 
= parts-per-billion; N0 2 = nitrite ion; N-NO 
= N-nitroso compound; ml/min = milliliters 
per minute; V = volts; nA = nanoamperes; GC 
= gas chromatography; TEA = Thermal Ener¬ 
gy Analysis; MS = mass spectrometry; ECD = 
electron capture detector; LCEC = liquid chro¬ 
matography-electrochemistry; TNT = 
2,4,6-trinitrotoluene; DNT = dinitrotoluene; 
NG = nitroglycerin; RDX = 1,3,5-trini- 


tro-1,3,5-triazacyclohexane; TETRYL 
= 2,4,6,N-tetranitro-N-methylaniline; NOT = 
nitrate ion; FIA = flow injection analysis; 
hv-EC = photolysis-electrochemical detection. 

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Binkley, R. W. and Koholic D. J. (1979). Photo¬ 
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cel Dekker, Inc., New York, in press, Chapter 
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28 


trace analysis. Recent advances in instrumenta¬ 
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Krull, I. S., Davis, E. A., Santasania, C., Kraus, 
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Krull, I. S. and Camp, M. J. (1980). Analysis of 
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McKinley, W. A. (1981). Application of the 
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Molnar, I., Knauer, H., and Wilk, D. (1980). 
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Popovich, D. J., Dixon, J. B., and Ehrlich, B. J. 
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selective detector in HPLC. J. Chromatogr. 
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tional Symposium on the Analysis and Detec¬ 
tion of Explosives, Federal Bureau of Investiga¬ 
tion (FBI) Academy, Quantico, Virginia, March 
29-31, 1983. 

Roston, D. A., Shoup, R. E., and Kissinger, 
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tion. Anal. Chem., 54:1417A-1434A. 

Scholten, A. H. M. T., Brinkman, U. A. Th., 
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Sherwood, G. A. and Johnson, D. C. (1981). A 
chromatographic determination of nitrate with 
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101 - 111 . 

Shoup, R. E. (1982). LCEC Bibliography: Recent 
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chemistry, BAS Press, Inc., Bioanalytical Sys¬ 
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Snider, B. G. and Johnson, D. C. (1979). A 
photo-electroanalyzer for determination of 
volatile nitrosamines. Anal. Chim. Acta, 106: 
1-13. 

Stevenson, R. L. and Harrison, J. (1981). Design 
and performance of a modular chromatograph 
for chromatography of anions. American Labo¬ 
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Yinon, J. (1977). Analysis of explosives. CRC 
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Boca Raton, Florida. 

Yinon, J. and Zitrin, S. (1981). The Analysis of 
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29 








SCREENING FOR ORGANIC EXPLOSIVES COMPONENTS BY HIGH 
PERFORMANCE LIQUID CHROMATOGRAPHY 
WITH DETECTION AT A PENDENT MERCURY DROP ELECTRODE. 


J. B. F. Lloyd 

Home Office Forensic Science Laboratory, 
Priory House, Gooch Street North, 
Birmingham, B5 6QQ, England 


ABSTRACT. The electrochemical detection of explosives components, separated 
by high performance liquid chromatography (HPLC), at a mercury film (thin lay¬ 
er) electrode (MFE) can be improved considerably both in ease of use and sensitiv¬ 
ity at a pendent mercury drop electrode (PMDE). The electrode characteristics are 
highly reproducible, the electrode may be renewed during or at the start of a 
chromatogram, and it is not subject to the contamination problems of the MFE. 
With 3 ^m-particle HPLC columns the detection limits for a wide range of nitrate 
and nitro compounds are at present 2-20 pg per 10 ^1 injected sample. These limits 
are approximately a tenfold improvement on those reported for the MFE tech¬ 
nique, and are comparable with those of electron capture detection in gas chroma¬ 
tography, compared with which technique the PMDE is superior in specificity. A 
facile clean-up procedure has been developed to enable the PMDE-HPLC tech¬ 
nique to be used for screening handswabs for traces of the explosives components. 
Examples of the application of the technique are presented. (British Crown copy¬ 
right reserved.) 


Mercury-Film Electrodes 

I wish to present some work arising from the 
important contribution that has been made to the 
chromatographic characterization of explosives by 
Dr Kissinger and his colleagues. 1 As Dr Kissinger 
has described, organic explosives components can 
be detected by the reduction current they generate 
at glassy carbon or mercury film on amalgamated 
gold electrodes. With fairly clean samples 1 have 
obtained results entirely in agreement with Dr 
Kissinger’s, and with excellent detection limits. 
However I ran into problems due to electrode con¬ 
tamination effects when samples from soiled 
handswabs were analyzed. 

Figure 1 shows an example from the high-per¬ 
formance liquid chromatography (HPLC) of a 
handswab, detected at a mercury film electrode 
(MFE). The passage of the sample through the de¬ 
tector has resulted in a disrupted base line. The ef¬ 
fect of further samples is additive, so that a suc¬ 
cession of them rapidly makes the system unusa¬ 
ble. Of course, the electrode can be stripped down 
and cleaned, which was done daily in any case, or 
the presumably deposited material can be dis¬ 


charged if the electrode potential is briefly set to 
zero. But either way a considerable loss in running 
time occurs. 

Mercury Drop Electrodes 

An obvious remedy here is to use a dropping 
mercury electrode—a polarographic detector—in 
which a new electrode can be formed as rapidly as 
several times a second. But with this electrode I 
found—as, indeed, have many others—that the 
sensitivity is severely restricted by the noise level 
generated in the formation and dislodgement of 
the mercury drops. 

A great improvement is to use a hanging mer¬ 
cury drop electrode, and to renew the electrode 
only when necessary. And an even further im¬ 
provement can be made with a so called “pend¬ 
ent” mercury drop electrode 2 , although 
“squashed” would be a more accurate descrip¬ 
tion. This is illustrated in Figure 2. It is a slightly 
modified version of a cell sold by Princeton Re¬ 
search. The original is intended to hang an unsup¬ 
ported drop from the Hg capillary in the eluent 
stream, which impinges on the drop from below 


31 


MFE -10 V 



min 

Figure 1. Chromatogram of a handswab extract detected at a 
mercury film electrode maintained at - 1.0 V vs. Ag/Ag Cl, 
and a chromatogram of 1 ng TNT under the same conditions. 
The chromatographic conditions are given in Table I. 

In the modified cell, the distance between the cap¬ 
illary tip and the eluent jet is continuously vari¬ 
able, and the jet orifice is opened-up to 0.8 mm. 
Hence, an increased drop-size relative to the 
tip-to-jet separation may be used; or a small drop 
can be introduced directly into the widened ori¬ 
fice. The effect of the modicication is to give some 
increase in absolute sensitivity in terms of sig- 
nal-to-noise ratios; but, most importantly, such 
drops can be left in position without any possibil¬ 
ity of their falling from the capillary tip—in con¬ 
trast to the hanging drop electrode. For a given 
tip-to-jet separation the optimum drop is slightly 
distorted due to mechanical compression and to 
the impinging eluate. 



Figure 2. The pendent mercury drop electrode (PMDE). The 
drop is located between the two opposed nozzles seen through 
the assembly’s porthole. The long dimension of the photo¬ 
graph represents 4 cm at the cell position. 

HPLC Conditions 

For HPLC the detector is used in conjunction 
with a 3-micron column with an aqueous methan¬ 
ol eluent buffered to pH 3.0 with phosphate (Ta¬ 
ble 1). I find the most efficient way to do the es¬ 
sential deoxygenation of the eluent reservoir is to 
keep the eluent under reflux continuously. This 
gives much lower levels of oxygen than a pro¬ 
longed nitrogen purge, although I do use a nitro¬ 
gen bleed to provide nucleation for the boiling sol¬ 
vent. I do not now include a chelating agent in my 
solvent, because this seems to increase the base 


32 













line signal, presumably because traces of heavy 
metals are eluted from the chromatographic 
equipment. 


Table 1. HPLC CONDITIONS 


Column packing 
Column dimensions 
Solvent 


Temperature 

Flow 

Detection 


ODS-Hypersil, 3-micron. 

Length, 15 cm; i.d., 4.5 mm. 
Methanol + aqueous phosphate 
(0.025 M, pH 3.0), 100 + 86 by 
volume. 

Ambient (>22°C) 

1 ml min~ * 

Pendent mercury drop (26 mg at a 
tip-to-jet separation of 0.9 mm; or 
3.2 mg at a separation of 0.4 mm) in 
a modified PARC 310 polarographic 
detector. The electrode potential was 
usually -1.0V vsAg/AgCl. 



Sample Deoxygenalion 

Apart from the eluent, samples too must be 
deoxygenated. There is a very simple way of doing 
this with small samples 3 . All that is needed is a 
modified glass hypodermic syringe. This is shown 
in Figure 3. The end of the syringe has been pulled 
down, and a Rheodyne-size needle expoxied into 
it. As Figure 4 shows, the injector is set upright 
with a nitrogen purge attached to the solvent waste 
line from the inject position of the injector, so that 
all that is necessary is to withdraw a portion of the 
sample into the syringe, set the syringe into the in¬ 
jector, pass nitrogen through it for 2 minutes and 
then make the injection in the usual way. 

Chromatograms—Standard Compounds 

This (Figure 5) is a chromatogram of a standard 
mixture of compounds. Each peak represents 
0.5ng of the 18 compounds, which are separated 
within eight minutes. All of the actual compounds 
are listed in Table 2 according to their numbering 
on the chromatogram. As the chromatogram 
shows, the drop is changed immediately before the 
start of the chromatogram. 

There are one or two points that must be made 
here concerning the use of 3-micron-particle col- 



Figure 3. Modified 1 ml syringe for sample deoxygenation and 
injection. 


33 


Figure 4. Sample, in modified syringe, during deoxygenation. 





umns. The sensitivity obtained from them, com¬ 
pared with 5-micron columns, is practically dou¬ 
bled provided efficient columns of the same theo¬ 
retical plate count are compared. This follows, of 
course, from the reduction in peak widths because 
the columns are shorter. But it cannot be too 
strongly emphasized that the solvent in which the 
sample is dissolved must closely match the eluent 
in composition. If it doesn’t, a catastrophic loss in 
resolution occurs. Provided care is taken over this, 
surprisingly large sample volumes can, if neces¬ 
sary, be injected without an unreasonable loss in 
resolution. This particular chromatogram (Figure 
5) is from a 10 -/j 1 injection. With 20-^1 injections 
excellent chromatograme are still obtainable. And 
even with 50-/ul some useful chromatography can 
still be done for the later-eluting peaks. A final 
point here: I find that the columns are just as easy 
to pack, and that they last just as well as those 
packed with 5-micron particles. 

Table 2. STANDARD EXPLOSIVES COMPOUNDS 


Numbered according to Fig. 5 

1 Nitroguanidine 

2 Octogen(HMX) 

3 Styphnicacid 

4 Picric acid 

5 Hexogen (RDX) 

6 Ethyleneglycol dinitrate (EGDN) 

7 Isosorbide dinitrate 

8 w-Dinitrobenzene 

9 Tetryl 

10 Nitrobenzene 

11 Nitroglycerine (NG) 

12 2,4,6-Trinitrotoluene (TNT) 

13 2,6-Dinitrololuene 

14 2,4-Dinitrotoluene 

15 o-Nitrotoluene 

17 w-Nitrotoluene 

18 Pentaerythritol tetranitrate (PETN) 


Detection Limits 

The detection limits of the technique vary, ac¬ 
cording to the compound, in the region 2-20pg. 
These (Figure 6) are examples of chromatograms 
of amounts of explosive compounds in this range. 
The lowest sensitivity here is for PETN, the high¬ 
est for the polynitro aromatic compounds. At the 
5 pg level, RDX and EGDN are obscured by resid¬ 
ual oxygen. 

The pressure pulsation of the pump used here, 
about 0.5%, evidently makes no contribution to 
the noise level, although if the background current 
is allowed to rise, e.g. due to traces of oxygen, a 
regular pulsation (depending in detail on the drop 


NITRO/ATE COMPOUNDS (0-5 ng) 
3-2 mg PMDE 4 



8 6 4 2 0 

min 


Figure 5. Chromatogram (PMDE) of standard explosives 
compounds. The identities of the compounds are given in 
Table 2. 

size) becomes apparent. The background current 
in these chromatograms was about 4.5 nA. 

These chromatograms are from 10-/ul injec¬ 
tions, hence the results in terms of concentration 
sensitivity are in the same region as electron cap¬ 
ture detection in gas chromatography. They are 
also much lower than the results originally reorted 
for thin layer electrodes, but I imagine similar re¬ 
sults would be obtained for both detectors given 
columns of similar efficiency. The important 
point here is that we now have a sensitive electrode 
that may be renewed the instant that this is re- 


34 












































quired, and that in any case the electrode is much 
less sensitive to contamination effects. 

Here (Figure 7) is the example from the thin 
film electrode experiment with hand swab mate¬ 
rial shown initially. It is compared here with a 
chromatogram detected at a PMDE, adjusted to 
give the same response with respect to TNT. Obvi¬ 
ously the problem of the disrupted base line is 
largely dealt with. Clearly there is some displace¬ 
ment, but this does not interfere in an analysis af¬ 
ter the initial peak, and the base line is completely 
restored when a new drop is formed for the next 
analysis. 

Sample Clean-up 4 

The comparison here (Figure 7) has been made 
with a sample that has not been cleaned-up, and 
both techniques give improved results with 
cleaned up samples. But even with these the same 
problems persist particularly with the thin film 
electrode. 

In one respect the HPLC system is more de- 


SENSITIV1TY LIMITS 
3-2 mg PMDE 



8 6 4 2 0 

min 


Figure 6. Chromatograms (PMDE) of standard compounds 
(Table II) in the region of their detection limits. 


manding in the type of sample it will accept than 
the more usual gas chromatography techniques. 
This arises because of the solvent-matching re¬ 
quirement that I have already mentioned. 

One obvious response to the problem is to use 
the HPLC solvent for swabbing. But it doesn’t 
work! The solvent composition changes during 
swabbing because of the accumulation of water 
from sweat and because of evaporation. Hence, 
any solvent on a swab must be removed. One may 
use dry swabs: these remove explosives from 
hands quite effectively. But, apart from the mois¬ 
ture problem, volatile explosives components are 
lost very rapidly from dry swabs. These compo¬ 
nents are also lost if an attempt is made to evap¬ 
orate the solvent from a swab. Another problem is 
that fats and oils are often present in large 
amounts, and need to be removed to protect the 
column from contamination. 

The solution to these problems is contained in a 
BAS centrifugal microfilter, as shown in Figure 8. 
The filter is packed with a mixture of 50 mg each 
of 10-micron alumina and 10-micron ODS— 
Spherisorb, and a piece of Viton sleeving is fitted 


HANDSWAB 



13 0 


min 

Figure 7. The same samples as in Figure 1 with a chro¬ 
matogram detected at a PMDE. 


35 


















































to the outside of the filter holder so that the as¬ 
sembly can be attached to a vacuum line. These as¬ 
semblies are made up in batches and stored away 
until required. Immediately before use ethanol is 
spun through the adsorbent. The swab is loosely 
inserted in the top of the filter, a silica gel trap is 
fitted to the top, and the lower end attached to the 
vacuum line so that a stream of dried air may be 
drawn through the swab and then through the ad¬ 
sorbent. With ethanol as a swabbing solvent the 
time-to-dryness is about Vi hour. This can be 
checked if necessary by weighing the assembly at 5 
minute intervals around the time when evapora¬ 
tion is thought to be nearing completion. 

If the swab is overwet, solvent may exude when 
the swab is pushed into the microfilter. In this case 
the surplus is removed, and the assembly inverted 
during the drying to avoid any solvent’s running 
onto the adsorbent. The surplus can be returned to 
the dried swab, which is then redried, although it 
is likely that sufficient sample for analysis will re¬ 
main on the swab in the first instance. 

The swab is now packed down onto the adsorb¬ 
ent, and the whole eluted with aqueous methanol 
(35 + 100, by volume) to give ca. 170 microlitres 
of extract. If this is collected in a tared tube, the 
composition of the extract is readily adjusted, us¬ 
ing its mass, to that of the eluent. 

During this process the following has occurred: 

1. The solvent remaining on the swab and in the 
adsorbent has been removed. 

2. Any explosives components that have volati¬ 
lized from the swab are mostly trapped out 
on the ODS-Spherisorb. 

3. During the elution, fatty and oily materials 
are trapped on the ODS-Spherisorb, whilst 
the explosives components run through. 

4. The alumina traps out much of the electroac¬ 
tive material that gives rise to the initial 
chromatography peak. 

A variety of recovery experiments made with 
used handswabs gave recoveries in the region 
80-90%, depending on the nature of the swab and 
on the compound concerned. 4 

Selectivity Considerations 

An example of the effect of the procedure in the 
reduction of the initial interference in a handswab 
extract is shown in Figure 9. Obviously, an appre¬ 
ciable number of compounds remain, in this ex- 
plosives-free sample, and these could probably be 
removed by more selective adsorbents. But the 
main objective so far has been the development of 
a screening procedure by which as many com- 




Adsorbent 


Viton sleeve 
Membrane 



Receiver 


Figure 8. Centrifugal microfilter (Bioanalytical Systems) as¬ 
sembly for extraction and clean-up of hand swabs. 

pounds as possible may be recognized. If more se¬ 
lective techniques are used, some of these are lost. 
It does in fact turn out that very few of the explo¬ 
sives components are overlapped by spurious 


36 






























peaks, and most handswabs are at least quali¬ 
tatively comparable in this respect. 

The situation is exemplified in Figure 10 where, 
on a cleaned-up handswab extract I have superim¬ 
posed a chromatogram due to 91 pg-amounts of 
each of 15 explosives components. This amount 
corresponds to 1 nanogam of each of them per 
swab. The only significant coincidences here are at 
the tetryl and the 2, 6-dinitrotoluene positions. 1 
have collected about 100 swabs from people, the 
majority of who were employed in manual work, 


26 mg PMDE 



Figure 9. Chromatograms (PMDE) comparing hand swab ex¬ 
tracts before (A) and after (B) clean-up. 


and find that above the level of 1 nanogram/swab 
the only frequent significant overlaps are as Fig 10 
indicates. 4 

Occasional overlaps occur with some other 
compounds, but with modified conditions it 
should be possible to exclude any possibility of 
confusion. I have examined the case of PETN spe¬ 
cifically, with the result shown in Fig. 11. At a po¬ 
tential of -1.0 V a peak occurs at the PETN posi¬ 
tion in this particular handswab extract. But at a 
potential of -0.6 V the handswab peak virtually 
disappear, whereas the PETN peak is reduced 
only to a third of its original intensity. Similar ex¬ 
periments are applicable to other compounds. 

Examples of chromatograms including an ex- 
plosives-containing hand swab are shown in Fig¬ 
ure 12. The hand swab was from a person who had 


26 mg PMDE 



Figure 10. Handswab extract, with a superimposed chroma¬ 
togram (PMDE) (dotted line) of 91 pg amounts of explosives 
components. 


37 












































min 

Figure 11. Chromatograms (PMDE) of a handswab extract (A 
and B) and PETN (C and D) with detection at - 1.0 V and 
- 0.6 V vs. Ag/Ag Cl. 



Figure 12. Examples of chromatograms (PMDE) from ex- 
plosives-containing samples: Hand swab collected after 3 
hours and an unknown number of handwashes following brief 
contact with Nobel-808, PE 4 and Cordtex; swab from a beer 
glass used 2/i hours and a hand-wash after PE-4 had been 
handled; and extraction assembly eluate after the vapour¬ 
sampling of debris containing or/Zto-nitrotoluene. 


briefly handled wrapped cartridges of Nobel-808 
and PE-4, and Cordtex detonating fuse. He was 
swabbed some 3 hours later, during which time he 
had washed his hands at least once. The chroma¬ 
togram shows the presence, as expected, of RDX, 
NG and PETN, in amounts varying between 
100-300 ng. 

The other chromatograms (Figure 12) are from 



Figure 13. Chromatograms (PMDE) from handswabs collect¬ 
ed at the indicated times after two shots had been fired from a 
Smith and Wesson model 10, .38 Special revolver. 


38 
























































a swab from a drinking glass used by a pei ^on who 
had handled PE-4 sometime earlier, and washed 
his hands—clearly RDX is present—and from an 
extract of the clean-up assembly after its use in a 
vapour sampling of some 1-day old debris left af¬ 
ter the explosion of a simulated terrorist device 
containing ortho-nitrotoluene. 

Figure 13 shows the results after a firearm had 
been discharged up to 2Vi hours earlier. These 
chromatograms represent ca. 5% of the material 
present on the swab, and hence 6 ng after the long¬ 
est time interval. 

The lowest levels of NG detected so far are in 
the region of 0.2 ng/swab. This was in some work 
on cardiovascular tablets. 5 In the future it should 
be possible to increase this by an order of magni¬ 
tude with the application of more specific 
clean-up techniques, as opposed to the gener¬ 
al-purpose ones used here. 


ACKNOWLEDGEMENT 

I am indebted to the Editor of the Journal of 
Chromatography for permission to reproduce a 
number of the Figures. 2 ' 4 


REFERENCES 

1. K. Bra tin, P. T. Kissinger and R. C. Briner. 
Anal. Chim. Acta, 1980, 130, 295. 

2. J. B. F. Lloyd. J. Chromatogr., 1983, 257, 
227. 

3. J. B. F. Lloyd. J. Chromatogr., 1983, 256, 
323. 

4. J. B. F. Lloyd. J. Chromatogr., 1983, 261, 
391. 

5. J. B. F. Lloyd. J. Forens. Sci, Soc., 1983, 23, 
307. 


39 












































































DETECTION AND ANALYSIS OF POLYNITROPHENOLS IN WATER 
BY REVERSED-PHASE ION-PAIR LIQUID CHROMATOGRAPHY 


John C. Hoffsommer and Donald J. Glover 
Naval Surface Weapons Center 
White Oak Laboratory 
Silver Spring, Maryland 20910 


ABSTRACT. The separation and quantitative analyses of mixtures of up to nine 
different polynitrophenols in water including both picric and styphnic acids by ion- 
pair liquid chromatography are described. Using Pic-A reagent (t-butyl ammon¬ 
ium phosphate) to produce the counter cation in methanol-water systems, quanti¬ 
tative results were obtained at phenol concentrations as low as 0.1 mg/liter (0.1 
ppm). Details of a preconcentration step for the analyses of polynitrophenols at 
the parts per billion (ppb) level are given. 


INTRODUCTION 

In the past, ammonium picrate (explosive D) 
has been widely used in a number of US Naval 
projectiles, but now its use has been largely dis¬ 
continued. Subsequently, ordnance items con¬ 
taining ammonium picrate have become obsolete 
and were demilitarized either by burning or by 
containment in various dump sites. In May, 1979, 
the Bureau of Medicine and Surgery, Department 
of the Navy, in response to its Assessment and 
Control of Installation Pollutants (ACIP) pro¬ 
grams at US Naval Stations, set a target interim 
maximum contaminant level (TIMCL) for nitro- 
phenols including ammonium picrate and picram- 
ic acid at 0.001 mg/L (1 ppB). To this end, in 
order to assess the extent that ammonium picrate 
(more specifically, picrate ion) remains contained, 
it is essential that reliable methods be available to 
measure low level picrate and other nitroaromatic 
phenoxide ions in ground water. 

As a class, the polynitroaromatic phenols are 
quite acidic and possess pKa values ranging from 
0.23 (2,4,6-trinitrophenol or picric acid) to 4.5 
(2-amino-4,6-dinitrophenol or picramic acid), 
and would be expected to exist almost entirely as 
the corresponding polynitrophenoxide anions in 
water. In addition, the salts of the polynitroaro¬ 
matic phenols would be expected to be readily sol¬ 
uble in water. Ammonium picrate, for example is 
soluble to the extent of about five grams per liter 
in water at room temperature. Furthermore, 
picramic acid has recently been reported by Wy¬ 


man et al to be a biotransformation product from 
picrate ion, while the formation of other com¬ 
pounds such as the isomeric dinitrophenols was 
suggested. 

Recently, in an excellent review article, Tom¬ 
linson et al. outlined reverse phase ion-pair liquid 
chromatography (LC) as a method for the anal¬ 
yses of ionic species in water. In this review the 
authors cite the work of Culbreth et al. who 
describe a procedure for the analysis of 4-nitro- 
phenol in the presence of 4-nitrophenol phos¬ 
phate. It would appear then that ion-pair LC 
would be an excellent choice for the detection and 
analysis of various polynitroaromatic phenols in 
water. The objective of the present study, there¬ 
fore, was to extend this ion-pair LC method for 
the analysis of picrate ion as well as other poly¬ 
nitroaromatic phenols at the parts per million 
(ppm) to the parts per billion (ppB) level in ground 
water. 

SIMPLIFIED PAIRED ION 
CHROMATOGRAPHY (PIC) THEORY 

In this discussion, a simplified PIC theory will 
be illustrated for ammonium picrate. In the water 
sample to be analyzed, ammonium picrate (I) is 
completely ionized according to equation (1), 
where Ph represents a phenyl ring. 

(1) PhfNCh), ONPb - Ph(NO:),(r + NHC 
(I) anion of 

( 1 ) 


41 


If tetrabutylammonium phosphate (II) (PIC (2) [(CH 9 ), N] 3 P0 4 ~^3(C 4 H y },N + + P0 4 3 

reagent, Waters Associates) is incorporated in the jj counter 

LC eluent (usually methanol/water mixtures), it is j on u 

also completely ionized according to equation (2). 


On injection of the water sample into the LC, the anion of I forms a neutral ion-pair complex with the 
counter ion II according to equation 3. 

(3) Ph(NO2) 3 0 + + N(C 4 HA - [PhfNO^O—N(C 4 H 9 )4] 

anion of I counter ion II neutral ion-pair complex 


Retention times of the polynitroaromatic phenols 
would be expected to vary with different substitu¬ 
ents associated with the anion of I, thus making 
separations on the reverse phase (RP) column pos¬ 
sible. In the absence of the PIC reagent, the poly¬ 
nitroaromatic phenoxide ions are not retained, 
hence not separated on the RP column. 

EXPERIMENTAL 

Polynitrophenol Solutions 

All nitrophenols were purified by recrystalliza¬ 
tion from the appropriate solvents, and melting 
points compared with known literature values. 
2,4,6-Trinitrophenol was also purified by re¬ 
crystallization of its ammonium salt. Standard 
solutions of each nitrophenol varying from 15 to 
350 mg/L were made by dissolving the nitrophen¬ 
ol directly in water and warming where necessary. 
Mixtures of nitrophenols were made from these 
standard solutions. 

Chromatographic Conditions 

A high performance liquid chromatograph 
(Hewlett-Packard, Model 1084A) equipped with a 
variable wavelength detector (HP Model 1030), 
variable volume injector, built-in processor for 
full integration calculation and printer-plotter 
capability was used with a 10 micrometer particle 
size RP-8 column, 25 cm long and 4.6 mm ID, 
maintained at 40°C. Unless stated otherwise, de¬ 
tector wavelength was 254 nm. 

RESULTS AND DISCUSSION 

For isocratic elution (Table 1), column flow was 
2.0 ml/min; mobile phase, 50/50 methanol/water, 
by volume, containing 5 x 10~ 3 M tetrabutyl-am- 
monium phosphate reagent buffered at pH 7.5 
(PIC A reagent, Waters Associates). Two bottles 
(30 mis) of PIC A reagent were dissolved in one 
liter of distilled water, diluted with another liter of 
HPLC grade methanol, and filtered through a 
0.45 micron filter (Millipore). The solvent was di¬ 


vided between reservoirs “A” and “B” of the 
chromatograph and degassed for one half hour at 
35 °C before establishing column flow. 

For gradient elution (Table 2) column flow was 
1.0 ml/min of a 45/55, by volume, mixture of 
methanol/water containing 5 x 10“ 3 M tetra¬ 
butylammonium phosphate reagent for 11 min¬ 
utes then increased to 50/50, by volume, metha¬ 
nol/water from 11 to 16 minutes. The mobile 
phase for gradient elution was prepared by dis¬ 
solving 15 mis of PIC A reagent in one liter of dis¬ 
tilled water, filtering through a 0.45 micron filter, 
and placing the filtrate in reservoir “A”. Reser¬ 
voir “B” was filled with a solution made by dis¬ 
solving 15 mis of PIC A in 100 mis of distilled wat¬ 
er and diluting with 900 mis of HPLC grade meth¬ 
anol. Both solutions were degassed at 35 °C for 
one half hour before establishing column flow. 

The RP-8 column was dedicated solely for the 
use with PIC A reagents and was thoroughly 
rinsed with methanol/water, 50/50, by volume, 
and allowed to stand in distilled water at the end 
of each day. 

Variable Wavelength Analyses 

In aqueous solutions buffered at pH 7.5, 
2-amino-4,6-dinitrophenol has two maximum 
absorptions at 310 nm and 410 nm, while, 
2,4,6-trinitrophenol exhibits a single maximum at 
355 nm. These maxima were not found to shift in 
the presence of 5 x 10 3 M tetrabutylammonium 
phosphate. Liquid chromatographic separations 
of these polynitrophenols were made with detector 
wavelength settings at 254 nm, 310 nm, 355 nm, 
and 410 nm. Area and peak height response were 
measured at each wavelength. Detector responses 
for 2-amino-4,6-dinitrophenol at 310 nm and 410 
nm were found to be 0.81 and 0.91 times the re¬ 
sponse at 254 nm, respectively. Detector responses 
for 2,4,6-trinitphenol at 355 nm were 1.3 times the 
response at 254 nm. At wavelengths lower than 
230 nm, absorption interferences of the solvent 
mobile phase were observed. Although no sub- 


42 




Table 1. VARIATION OF RETENTION TIMES AND DETECTOR RESPONSES IN THE ANALYSES OF POLYNITRO- 
PHENOLS IN WATER BY ION-PAIR LIQUID CHROMATOGRAPHY 

Retention b Detector Response c 

Phenol 3 Time, min Area Counts/ng mm/ngd 


(water) 

1.5 

— 

— 

2-amino-4,6-dinitro- 

3.06 

133 ± 3(8) 

1.56 ± 0.04 (8) 

2,4-dinitro- 

4.26 

104 ± 2(8) 

0.86 ± 0.02(8) 

2-methyl-4,6-dinitro- 

6.34 

92 ± 4 (8) 

0.54 ± 0.01 (8) 

2,4,6-trinitro- 

7.67 

103 ± 2(6) 

0.51 ± 0.01 (9) 

3-methyl-2,4,6-trinitro- 

11.5 

89 ± 3 (6) 

0.30 ± 0.01 (8) 


(a) Concentration range, 1 to 15 mg/L in water; 100 microliter injection. 

(b) Isocratic elution; mobile phase, 50/50 methanol/water, by volume, containing 5 x 10- 3 M tetrabutylammonium phosphate 
buffered at pH 7.5; flow, 2.0 ml/min; RP-8 column, 10 micrometer particle size, 25 cm x 4.6 mm ID. 

(c) Detector wavelength, 254 nm; values in parentheses are number of determinations; ± values are standard deviations for the de¬ 
tector responses observed. 

(d) Height sensitivity, 8 x 10-5 AU/mm. 


stantial changes in detector responses were ob¬ 
served at wavelengths other than 254 nm, the 
measurable differences in response factors at these 
different wavelengths could serve as a positive 
means of compound identification. 

Detection Limits 

In order to be able to detect a particular nitro- 
phenol in water, the sample signal must be at least 
twice the noise level at any given detector sensitiv¬ 
ity. From Table 1, the height response for 
2-amino-4,6-dinitrophenol was found to be 1.56 
mm/ng at a detector sensitivity of 8 x 10~ 5 
AU/cm, where the noise level was ± 1 mm. 
Therefore, the sample peak height must be at least 


2 mm which corresponds to 1.3 ng, and for a 100 
microliter injection is 0.013 mg/L (lower detection 
limit for 2-amino-4,6-dinitrophenol). Since the 
height response for 2,4,6-trinitrophenol is 0.51 
mm/ng under the same conditions, the detection 
limit of this nitrophenol may be calculated to be 
0.040 mg/L (lower detection limit for 2,4,6-trini¬ 
trophenol). 

Preconcentration and Analysis at the Parts Per 
Billion (ppB) Level 

At first, an extraction scheme appeared attrac¬ 
tive, whereby the nitrophenol would be extracted 
from the water sample after pH adjustment into a 
small volume of benzene, and then back-extracted 


Table 2. SEPARATION OF AN AQUEOUS NINE COMPONENT POLYNITROPHENOL MIXTURE BY ION-PAIR LIQ¬ 
UID CHROMATOGRAPHY 



Retention 1 ) 

Relative Detector Response* 

Phenol Mixture 3 

Time, min 

Area Counts/ng 

mm/ng 

water 

3.0 

— 

— 

3-hydroxy-2,4-dinitro- 

5.32 

0.44 

0.49 

3-hydroxy-2,4,6-trinitro- 

6.11 

0.44 

0.55 

2-amino-4,6-dinitro- 

7.13 

1.04 

1.0* 

3-hydroxy-4,6-dinitro- 

8.52 

0.32 

0.28 

2,6-dinitro- 

9.46 

0.79 

0.57 

2,4-dinitro- 

10.5 

0.79 

0.50 

2-methyl-4,6-djnitro- 

16.8 

0.69 

0.31 

2,4,6-trinitro- 

20.0 

0.78 

0.39 

3-methyl-2,4,6-trinitro- 

25.8 

0.69 

0.29 


(a) Compounds present in concentration range, 2 to 6 mg/L; 100 microliter injection. 

(b) Elution conditions: isocratic for 11 min; flow 1.0 ml/min; mobile phase 45/55 methanol/water, by volume, then gradient elu¬ 
tion to 50/50 methanol/water from 11 to 16 min, then isocratic to 30 min. RP-8 column, 25 cm x 4.6 mm ID, 10 micrometer 
particle size; mobile phase containing 5 x 10 3 " M tetrabutylammonium phosphate at pH 7.5. 

(c) Detector wavelength, 254 nm. 

(d) Detector response, 255 area counts/ng. 

(e) Detector response, 1.63 mm/ng at a sensitivity of 8 x 10- 5 AU/cm. 


43 







from the benzene into another small volume of 
water containing sodium bicarbonate prior to LC 
analysis. However, the distribution coefficients of 
the nitrophenols between benzene and water at a 
given pH were not large enough to effect a real 
concentration of 100 to 1 or 50 to 1. The distribu¬ 
tion coefficients of 2-amino-4,6-dinitrophenol 
and 2,4,6-trinitrophenol between benzene and 
water were determined to be 31 (at pH 2.5) and 52 
(at pH 1.3), respectively. In addition, there was 
another complication. At pH values lower than 
pH 2, the amine group of 2-amino-4,6-dinitro- 
phenol became protonated in water and was not 
extracted by benzene. 

Another attempt was made to concentrate the 
polynitrophenol on a Bondapak C-18 Porasil Sep 
Pak (Waters Associates) cartridge. Fifty to one 
hundred milliliters of an acidified water sample 
(pH adjusted to 2.5) containing a 1 ppB mixture 
each of picrate and picramate ions was passed in 
increments through the cartridge. The cartridge 
was then extracted with 2.0 ml of HPLC methanol 
and the methanol extract was evaporated to a 
measured volume of approximately 0.5 ml prior to 
LC analysis. Although some concentration of the 
nitrophenols was achieved with this procedure, 
overall recoveries of the nitrophenols were only 
around 60 ± 10% at the 1 ppB level. This is un¬ 
doubtedly due to the marked tendency of both ni¬ 
trophenols to ionize and to be “washed” off the 
C-18 cartridge. 

Another method, currently under investigation, 
appears to be superior. One milliliter of PIC A 
reagent was added to 100 mis of the aqueous sam¬ 
ple to be analyzed, and then the mixture was ex¬ 
tracted with 10 mis of methylene chloride. By this 
procedure, essentially 100% of the polynitrophen¬ 
ol was extracted into the methylene chloride as the 
neutral ion-pair complex. The methylene chloride 
was then carefully evaporated to dryness, and the 
residue taken up in 0.40 ml of methanol/water, 
50/50, by volume, containing phenolphthalein as 
an internal standard. Using this method, picrate 
ion has been analyzed at the 0.6 to 1.0 ppB level 
with an overall recovery of 103 ± 15%. 

The procedures outlined here can be readily 
used with most conventional liquid chromato¬ 
graphs employing the usual standard 254 nm UV 



Figure 1. PIC Separation of 2-Amino-4,6-Dinitrophenol (Pi- 
cramic Acid) and 2,4,6-Trinitrophenol (Picric Acid) at 1 PPM 
Level. 


detector for the analyses of polynitroaromatic 
phenols at the ppB level with a simple preconcen¬ 
tration step. It may be possible, however, with 
more sophisticated detectors such as the thermal 
energy analyzer (TEA) detector or by a phosphres- 
cence spectroscopic technique, that these ppB lev¬ 
els could be reached directly without a preconcen¬ 
tration step. 

REFERENCES 

Culbreth, P. H., Duncan, I. W. and Burt is, C. A. 

(1977). Clin. Chem., vol. 23/12, p 2288. 
Tomlinson, E., Jefferies, T. M. and Riley, C. M. 

(1978). J. Chromatog., vol. 159, p. 315. 

Wyman, J. F., Guard, H. E., Won, W. D. and 
Quay, J. H. (1979). Appl. Microbiol., vol. 
37/2,p222. 


44 












LIQUID CHROMATOGRAPHY/ELECTROCHEMISTRY DETERMINATION OF 
EXPLOSIVES: IMPROVED PERFORMANCE USING LOW DEAD VOLUME 

MULTIPLE ELECTRODE TRANSDUCERS 


Peter T. Kissinger 

Department of Chemistry, Purdue University, and Bioanalytical Systems, 

W. Lafayette, IN 47906, U.S.A. 

ABSTRACT. Most commonly used explosive substances are electrochemically 
reducible at modest negative potentials (below - 1.0 volt vs. Ag/AgCl). As a re¬ 
sult, electrochemistry provides excellent selectivity for these substances because 
very few naturally occurring materials contain nitro groups. The combination of 
reverse phase chromatography with electrochemical detection therefore provides a 
unique opportunity to determine very small amounts (typically 1 ng) of various ex¬ 
plosive substance. In this presentation, the principles and experimental practice of 
LCEC will be reviewed with specific reference to optimization of the quantitation 
and identification of individual explosive materials. A series dual-electrode scheme 
was applied to the detection of explosive compounds in standards, gunshot residue 
and environmental samples. The series dual-electrode thin-layer transducer can ex¬ 
tend the specificity and detection limits (for compounds reduced at higher energies) 
of the amperometric detector and can also provide better assurance of peak identi¬ 
ty. In the case of polynitro aromatic explosives, the detection limits obtained with 
the dual-electrode transducer (signal measured at the downstream electrode) were 
higher by a factor of 3-4 than with a single electrode transducer because the de¬ 
crease in the baseline noise did not fully compensate for the decrease in the elec¬ 
trolysis current at the downstream electrode. Operating the reductive LCEC system 
with a series dual-electrode transducer allows a direct injection of the sample solu¬ 
tion without the need to remove dissolved oxygen prior to the injection. The de¬ 
scribed methodology permits detection of explosive compounds at detection limits 
below 10 ppb, depending on the particular compounds. LCEC appears to have sig¬ 
nificant advantages vs. gas phase techniques for the determination of nitro-based 
explosives for environmental and forensic purposes. The primary future direction 
is to improve reliability for the occasional user of the technique. When large num¬ 
bers of samples need to be processed on regular basis, the method is well estab¬ 
lished and few problems are encountered with dedicated instrumentation. 


INTRODUCTION 

The first practical liquid chromatography/elec¬ 
trochemistry (LCEC) experiments were carried 
out in early 1972. The technological developments 
followed the need to solve an important problem 
in neuropharmacology. Determination of catecho¬ 
lamine and serotonin neurotransmitters in brain 
tissue using such diverse techniques as fluores¬ 
cence, gas chromatography/mass spectrometry, 
and various radiochemical techniques left much to 
be desired. LCEC appeared to be a good solution 
to some of the problems and after a decade of de¬ 


velopment, nearly a thousand publications have 
appeared. The primary attributes of the technique 
are its good selectivity, low detection limits, wide 
applicability (especially vs. fluorescence), and low 
cost (especially vs. GCMS and radiochemical pro¬ 
cedures). 

In recent years a number of new applications 
(enzyme activity measurements, GABA, acetyl¬ 
choline, NADH, pterins, explosives etc.) have 
been developed. Multiple-electrode LCEC detec¬ 
tion systems are now available which permit signi¬ 
ficantly improved performance. The new trans- 


45 


ducers are compatible with short, high speed col¬ 
umns and longer microbore columns. With mul¬ 
tiple electrode LCEC the identification of individ¬ 
ual substances can be confirmed and the selectivity 
can be much improved. In addition, better detec¬ 
tion limits can be achieved for some compounds. 
The latest developments in LCEC technology will 
be briefly described with respect to (1) multiple 
working electrodes, (2) “high speed” columns, 
and (3) post-column reactions. All three areas 
provide opportunities for further application of 
LCEC to explosives. 

ELECTROCHEMISTRY OF EXPLOSIVE 
SUBSTANCES 

LCEC of reducible substances is now very high¬ 
ly developed and is in widespread use for a variety 
of substances [Shoup (1982); Bratin, Kissinger, 
and Bruntlett (1981)]. A large percentage of the 
applications for reductive LCEC have involved ni- 
tro compounds which are generally well behaved 
electrochemically. Nitro aromatic, nitramine, and 
nitrate ester explosives are all good LCEC candi¬ 
dates. In the late 1970’s our laboratory at Purdue 
began an extensive study of the potential use of 
LCEC for monitoring explosives in gun shot resi¬ 
due, post-blast debris, environmental samples, 
and biological fluids. Much of the early work has 
been summarized in the literature [Bratin, Kissin¬ 
ger, Briner, and Bruntlett (1981)] and will not be 
reported here. Several groups (see other papers in 
this volume) have continued this effort and it is 
now clear that LCEC is a very viable approach to 
determination of explosives in many situations. 
The primary difficulty with the technique relates 
to the lack of education of the forensic science 
community in electrochemical methods. Perhaps 
equally important is that few laboratories encoun¬ 
ter enough samples to keep the instrumentation in 
constant use, a requirement for reliable and cost 
effective operation. 

MULTIPLE ELECTRODE LCEC 

Electrochemistry in thin layers of solution is a 
very highy developed field of electroanalytical 
chemistry. The thin-layer geometry is ideal for 
LCEC in that it provides a very low volume trans¬ 
ducer which can faithfully reproduce the shape of 
concentration profiles (“peaks”) eluting from 
very efficient LC columns. Figure 1 illustrates the 
most popular LCEC detector cell. The thin-layer 
channel is defined by a gasket held between the 


upper block (a stainless steel auxiliary electrode 
with low dead volume fittings) and the lower block 
(an inert polymeric material containing one or 
more working electrodes at which the reactions of 
interest occur). The effective dead volume can be 
made less than 1 /jL, a very difficult task for op¬ 
tical detectors. Routine determination of 1 pmole 
of an analyte is generally very straightforward and 
often 0.1 pmole or less can be quantitated in opti¬ 
mized procedures. 

The simultaneous use of two working electrodes 
greatly improves both the qualitative and quanti¬ 
tative aspects of an LCEC experiment. Electrodes 
of the same or different materials may be used and 
the electrode potentials may be independently con¬ 
trolled. In the “parallel mode” the compounds 
elutng from the column pass over each electrode at 
the same time. The following applications are 
quite useful: 

1. The ratio of currents monitored at each elec¬ 
trode can provide confirmation of peak identity 
and purity. 

2. Oxidations and reductions can be carried out 
simultaneously. This saves time and enhances se¬ 
lectivity. This can be ideal for compounds present 
in several different redox states (e.g. pterins). 

3. Signals from low and high potential reac¬ 
tions can be recorded simultaneously, providing 
both greater selectivity and wider applicability in a 
single experiment. 

4. A difference signal can be plotted to subtract 
out “common mode” information while enhanc- 


R 



46 


































ing detection of the desired compound. 

In the “series mode’’ the lower block is rotated 
90° in relation to the flow stream. Products of the 
upstream electrode reaction can be detected down¬ 
stream. If an oxidation is carried out upstream a 
reduction is accomplished downstream and vice 
versa. The following applications are popular: 

1. The ratio of currents monitored at each elec¬ 
trode can provide confirmation of peak identity 
and purity. 

2. Selectivity is enhanced at the downstream 
electrode because compounds with chemically ir¬ 
reversible reactions upstream are discriminated 
against. 

3. The upstream electrode can “derivatize” 
compounds to enhance detectability at the down¬ 
stream electrode. Overall selectivity and detection 
limits can be greatly improved. 

4. Dissolved oxygen can be discriminated 
against, simplifying LCEC of compounds that or¬ 
dinarily would require mobile phase deoxygena¬ 
tion (e.g. nitrocompounds). 

5. “Common mode” currents can be discrim¬ 
inated against by taking the difference between the 
two signals. 

Both series and parallel dual electrode LCEC 
provide many opportunities for study of explo¬ 
sives because of the wide range of redox properties 
involved, including some compounds that are rela¬ 
tively difficult to reduce (e.g. nitramines, nitrate 
esters) and some that reduce extremely easily (e.g. 
picric acid). 


“HIGH SPEED” COLUMNS FOR LCEC 

Short LC columns (typically 3-10 cm) packed 
with small particles (typically 3/um) can provide 
very high resolution separations in a few minutes. 
For example, Figure 2 illustrates the separation of 
17 neurochemicals in under 8 minutes using an ex¬ 
perimental 10 cm reverse phase column. This tech¬ 
nology requires modification of a conventional 
LCEC system to minimize dead volume, but these 
modifications are quite straightforward and pre¬ 
sent no unusual problems [Shoup (1983)]. This de¬ 
velopment presents a great opportunity for solving 
certain types of problems, but by no means re¬ 
places LCEC experiments using more convention¬ 
al 25-30 cm columns. With respect to explosives, 
short high speed columns afford detection limits 
below 0.1 pmole, however, in our experience it is 
rare that such low detection limits are necessary 
for forensic work. Nevertheless, work at the 1 



Figure 2. Separation of neurochemical standards. 


pmole level has become extremely reliable for rou¬ 
tine purposes. 


POST-COLUMN REACTIONS IN LCEC 

Post-column chemical reactions coupled to 
electrode reactions are also expanding the range of 
LCEC applications. Figure 3 illustrates four con- 





OTHER CATALYST 





IN SITU ECHEM 
REAGENT PREP 



"ECHEM DERIVATIZATION" 


EXAMPLE: 


OXIDASE ENZ. (H^) 


DEHYDROGENASE (NADH) 


RXN OF Br 2 WITH DBL BOND 


DUAL SERIES LCEC 
(RSSR— 2RSH) 


Figure 3. Post-column strategies for LCEC. 


47 




















































figurations. In A a reagent is added, mixed, and 
reacted in a delay line followed by electrochemical 
detection. A superb example of this is the determi¬ 
nation of acetylcholine in brain tissue by re¬ 
verse-phase LCEC. Acetylcholine esterase and 
choline oxidase are mixed in and the detection 
process proceeds as follows: 

acetylcholine -*■ choline + acetic acid 

choline -*■ betaine + H 2 0 4- 2H 2 0: 

The peroxide is detected electrochemically at a 
platinum electrode [Potter, Meek, and Neff 
(1982)]. 

In B, a catalyst in immobilized and a cofactor is 
detected. For example, using a dehydrogenase en¬ 
zyme an alcohol can be detected indirectly by 
monitoring the turnover of NAD to NADH, the 
latter being ideal for electrochemical detection. In 
C an upsteam electrode generates a reagent (e.g. 
Br 2 from Br in the mobile phase) which reacts with 
a nonelectroactive compound (e.g. an unsaturated 
fatty acid) and the decrease in reagent concentra¬ 
tion is monitored downstream. In D, the analytes 
of interest are converted at an upstream electrode 
into a product which is more selectively detected 
downstream. Examples include reduction of a ni- 
tro compound to a hydroxylamine, reduction of a 
disulfide to a thiol, and reduction of a nitrate ester 
explosive to generate the nitrite ion. In all three ex¬ 
amples, the reduction product is detected by oxi¬ 
dation and the resulting anodic current is used for 
quantitation of the original material. 

It was the intention of this brief review to indi¬ 
cate that LCEC technology is advancing rapidly. 
The technique is far more reliable and now exhib¬ 
its significantly better sensitivity and detection 


limits. When coupled with pre- and post-column 
reactions the range of applicable compounds has 
been dramatically increased. The improvements 
enhance our original publication on LCEC of ex¬ 
plosives [Bratin et. al (1981)], but do not inval¬ 
idate any aspect of our earlier work. The prin¬ 
ciples and applications of LCEC have been thor¬ 
oughly reviewed in recent text [Kissinger (1984)]. 

ACKNOWLEDGEMENT 

The author wishes to thank Dr. Ron Shoup and 
his group at Bioanalytical Systems R&D for their 
continuous input of new ideas. Prof. LeRoy Blank 
of the University of Oklahoma is thanked for his 
contribution of Figure 2 and the innovative work 
that made it possible. 

REFERENCES 

Bratin, K., Kissinger, P. T., Briner, R. C., Brunt- 
lett, C. S, Anal. Chim. Acta 130, 295-311 
(1981). 

Bratin, K., Kissinger, P. T., and Brunt let t, C. S. 
J. Liquid Chromatogr., 4(10), 1775-1795 

(1981). 

Kissinger, P. T. Ed., Liquid Chromatography/ 
Electrochemistry: Principles and Applications, 
BAS Press, W. Lafayette (1984). 

Potter, P. E., Meek, J. L., Neff, N. H. 1982 So¬ 
ciety for Neuroscience Abstracts, No. 143.8. 
Shoup, R. E. Current Separations, 5(1), 7-10 
(1983). 

Shoup, R. E. Ed., Recent Reports on Liquid 
Chromatography/Electrochemistry, BAS 
Press, W. Lafayette (1982). 


48 


CHARACTERISTICS OF PLASTICS, POLYMURS 
AND EXPLOSIVES BY DIRECT SIZE 
EXCLUSION CHROMATOGRAPHY 

Kenneth Alden 
Waters Associates 


Paper No. 5 not submitted for publication. 


49 




























































GENERAL ANALYSIS 































IDENTIFICATION OF REACTION PRODUCTS IN RESIDUES FROM 

EXPLOSIVES 


A. D. Beveridge, W.R.A. Greenlay andR. C. Shaddick 
Royal Canadian Mounted Police, 

Forensic Laboratory, 

Vancouver, B.C. 


ABSTRACT. Reaction products and unreacted components in explosive residues 
have been identified in test explosions of: (i) “home-made” explosive mixtures of 
oxidisers and fuels, (ii) high explosives of the “water-gel” type. The 
“home-made” explosives were two-component mixtures of oxidisers (chlorates, 
perchlorates, nitrates) with fuels (sugar, sulphur, aluminum) and were ignited both 
confined and unconfined. The high explosives were sticks of “water-gel” explo¬ 
sive produced by two different manufacturers. The composition of residues from 
these explosives was compared to residues from dynamite. Residues were systemat¬ 
ically analysed by routine solvent extraction methods and analytical procedures. 


Previous work (Beveridge et at. (1975)) has de¬ 
scribed the analysis and identification of residues 
from the explosion of dynamites, plastic explo¬ 
sives and some chemical mixtures, primarily 
smokeless powders. This work extends the explo¬ 
sives studied to the “water-gel” type of high ex¬ 
plosive and to a wider range of “home-made” 
chemical mixtures. 

The objective of this work was two-fold: to ex¬ 
pand our analytical data base (Beveridge, (1978)) 
and hence improve interpretation of casework 
analyses, and to continue testing the effectiveness 
of the analytical scheme for explosive residues. 

EXPERIMENTAL 
Chemical Mixtures 

Chemicals used were reagent grade sodium 
chlorate, sodium nitrate, potassium chlorate, po¬ 
tassium perchlorate, potassium nitrate, calcium 
nitrate, sulphur, aluminum powder and charcoal. 
Domestic table sugar was used for sucrose. The 
chemicals were carefully ground by hand prior to 
mixing. 

Burning was carried out on both confined and 
unconfined mixtures. Unconfined burning was 
conducted in an evaporating dish in a fume hood 
using a nitrocellulose-based fuse for initiation. 

Confined burning was conducted at an explo¬ 
sives range using ca.70g of chemicals in steel pipes 
(4-5 inches long, 1 inch inside diameter, % inch 


wall thickness) with threaded end-caps. One 
end-cap had a / 8 inch hole through which were in¬ 
serted the wires of the initiator, an electric squib. 
The confined burns were conducted in steel cylin¬ 
ders (1-2 feet diameter, 0.5-1 inch wall thickness) 
with flat circular caps (2 inches thick) on top and 
bottom. This permitted satisfactory recovery of 
pipe fragments. The cylinders were washed with 
water and acetone between tests. Residue recovery 
was restricted to the pipe fragments, using solvent 
extraction (acetone and water). 

“Water-gel” Explosives 

Explosives used were “Powermex 500”, manu¬ 
factured by Canadian Industries Ltd., and 
“Tovex 5000 SD”, manufacturer by Du Pont. 
Each explosive was an aluminised gel in a plastic 
tube. 

Initiation was by No. 6 electrical blasting cap. 
Residues were collected from various surfaces in¬ 
cluding wood, cloth and steel. 

Methods 

The scheme used in the analysis of the explo¬ 
sives and their residues was the systematic applica¬ 
tion of solvent extraction, microscopy, infrared 
spectroscopy (IR), thin-layer chromatography 
(TLC), X-ray diffraction (XRD), emission spec¬ 
troscopy (ES) and chemical tests as reported pre¬ 
viously in detail (Beveridge et at, (1975)). For cer¬ 
tain applications, other methods have been 


53 


added—a scanning electron microscope with ener¬ 
gy dispersive X-ray analyser (SEM/EDX) for 
qualitative elemental analyses (including chlorine 
and sulphur), and gas chromatography (GC) and 
gas chromatography/mass spectroscopy (GC/MS) 
of trimethyl silyl (TMS) ether derivatives of sug¬ 
ars. 

SEM/EDX 

A Semco (Bausch & Lomb) Nanolab 7 SEM 
equipped with a Kevex 7000/77 Energy Dispersive 
X-ray spectrometer was used. 

Gas Chromatography 

N-trimethylsilylimidazole in pyridine, marketed 
by the Pierce Chemical Company as TR1-SIL 
‘Z’® , was used to silylate sugars in order to facil¬ 
itate analysis by gas chromatography. The stand¬ 
ard reaction conditions supplied by the manufac¬ 
turer were used. One milliliter of TR1-SIL ‘Z’® 
was added to 15 milligrams of the sugar standards 
glucose, fructose and sucrose and to 50-100 milli¬ 
grams of aqueous extracted residues. The reac¬ 
tions were conducted in “Reactivials”® . The 
samples were heated to 60-70 °C for approx¬ 
imately 45 minutes or until the sugar had dis¬ 
solved. 

GC analysis was performed on a Perkin Elmer 
model 900 gas chromatograph equipped with 
flame ionization detectors, using a 12 foot x /, 
inch stainless steel column packed with 3% OV-1 
coated on 80/100 mesh Chromasorb W(HP). 

Gas Chromatography/Mass Spectroscopy 
(GC/MS) 

A Finnigan model 3100 quadrupole/mass spec¬ 
trometer interfaced to a Finnigan 9500 gas chrom¬ 
atograph was used. The mass spectrometer was 
operated at 70 eV. The GC contained a 6 foot by 
Va inch glass column packed with 3% OV-1 on 
80-100 mesh Chromasorb W(HP). 

RESULTS AND DISCUSSION 
(a) Chemical Mixtures 

The mixtures were, with two exceptions, 
two-component combinations of oxidisers (per¬ 
chlorate, chlorate, nitrate) with fuels (sucrose, sul¬ 
phur, aluminum) which were burned unconfined, 
and confined in pipes. Appendix “A” provides 
details of the specific mixtures used and the com¬ 
plete analytical results. 

The study focussed on the condensed reaction 
products formed by each oxidiser and fuel. The re¬ 
action product compositions were found to be in¬ 


dependent of the degree of confinement. These re¬ 
sults are summarised in Table 1. The principal ob¬ 
servations made during the tests are described, 
firstly for the oxidisers and then for the fuels. 


TABLE 1. CONDENSED REACTION PRODUCTS FROM 
BURNING OF OXIDISER/FUEL MIXTURES 


Oxidiser 

Perchlorate (Cl0 4 ) 

Chlorate (CIO 3 ) 
Nitrate (NO 3 ) 

Fuel 

Sucrose (C 12 H 22 OH) 


Sulphur(S) 
Aluminum (Al) 


Condensed Reaction Products 

Chloride (Cl ) (major product) 

Chlorate (CIO 3 ) (minor product) 
Chloride (Cl ) 

Nitrite (N0 2 ) 

Carbonate (CO 3 2 -) 

Bicarbonate (HCO 3 ) 

Sulphate (SO 4 2 -) 

Aluminum Oxide (AI 2 O 3 ) 


(i) Perchlorates 

The perchlorates underwent a rapid and intense 
reaction with each of the fuels used. When con¬ 
fined, the reactions shattered the pipes into small 
fragments. 

The major reaction product, produced in high 
yield, was the alkali metal chloride, identified by 
XRD. Also, a small quantity of chlorate was pro¬ 
duced and was identified, along with traces of 
unreacted perchlorate, by 1R and XRD (Appendix 
“A”, nos. 1 &2). 

(ii) Chlorates 

Like the perchlorates, the chlorates reacted vig¬ 
orously with each of the fuels. The confined reac¬ 
tions split the pipes longitudinally, but produced 
less fragmentation than did the perchlorates. The 
only product recovered was a high yield of alkali 
metal chloride, identified by XRD (Appendix 
“A”, nos. 3 thru 6). 

(Hi) Nitrates 

In binary mixtures, nitrates reacted less violent¬ 
ly with the fuels than did the perchlorates or chlo¬ 
rates. When confined, the damage to the pipe was 
limited to blowing a hole in, or blowing off, one 
end cap. The reaction product was nitrite, identi¬ 
fied by spot test and by 1R (Appendix “A”, nos. 7 
& 8). Attempts to burn a calcium nitrate mixture 
were unsuccessful due to its highly hygroscopic 
nature (Appendix “A”, no. 9). 

In a ternary mixture with sulphur and charcoal 
(black powder), burning of the confined mixture 
split the pipe longitudinally and produced damage 
similar to chlorate binary mixtures. The principal 
reaction product was nitrite (Appendix “A” nos. 
10 and 11). 


54 



(iv) Sucrose 

In the pure dry state, sucrose was readily identi¬ 
fied by XRD, IR or the polarising microscope. 
However, evaporation of aqueous extracts of resi¬ 
dues containing sucrose tended to yield syrups 
rather than solids, requiring an alternate method 
for identification. Formation of the trimethylsilyl 
ether derivatives (TMS) of sucrose, which were 
analysed and identified by gas chromatog¬ 
raphy/mass spectrometry (GC/MS), was found to 
be a suitable procedure. One interesting facet of 
the sucrose reactions was the identification, by the 
TMS-GC method, of glucose and fructose in the 
residue from the unconfined burning of potassium 
perchlorate and sucrose. No condensed reaction 
product was observed, and it seems more likely 
that these monosaccharides were produced by hy¬ 
drolysis of the sucrose on extraction rather than 
by the burning reaction (Appendix “A” no. 2). 

The nature of the reaction products of sucrose 
was dependent on the oxidiser used. When burned 
with chlorates and perchlorates, sucrose produced 
virtually no condensed reaction product. In these 
reactions, the product was principally the alkali 
metal halide, and thus was derived almost entirely 
from the oxidiser with chlorate only, a spot test 
indicated the possible presence of carbonate or bi¬ 
carbonate, but neither could be confirmed by IR 
or XRD (Appendix “A” nos. 3, 4). 

On the other hand, when burned unconfined 
with nitrates, the sucrose produced a major pro¬ 
portion of the condensed reaction product. In two 
separate reactions of potassium nitrate and su¬ 
crose, the reaction products obtained were potas¬ 
sium carbonate and potassium bicarbonate 
(identified by XRD and IR) along with nitrite (Ap¬ 
pendix “A” nos. 7, 8). 

(v) Sulphur 

The principal reaction product of sulphur when 
burned with an oxidiser was sulphate. This was 
identified by IR or XRD (Appendix “A”, nos. 5, 
10 , 11 ). 

The composition of the solid formed by evapo¬ 
ration of solutions containing carbonate and sul¬ 
phate ion was dependent on the cation. XRD 
showed that potassium sulphate and carbonate 
were recovered unchanged from aqueous solution. 
With the sodium salts, however, when the mole ra¬ 
tio of sodium carbonate to sulphate was in the 
range 0.2 to 0.5:1, the solid isolated by evapora¬ 
tion was identified by XRD as sodium carbonate 
sulphate (Na 2 C 03 ) n (Na 2 S0 4 )ti-n) (n = 0.2 to 0.5). 
This compound and its formation were discussed 


in previous work with respect to aqueous extracts 
of dynamite residues (Beveridge et al. (1975)). 

In this study, sodium carbonate sulphate was 
identified by XRD as the product of aqueous ex¬ 
traction of residue from the unconfined burning 
of the ternary mixture of sodium nitrate, sulphur 
and carbon. Prior to aqueous extraction, XRD of 
the residue showed it to be a carbonate-stabilised 
form of sodium sulphate (Beveridge et al. (1975)). 
That is, the product of aqueous extraction did not 
have the same X-ray diffraction pattern as the 
unextracted residue. 

That certain dynamites and sodium ni¬ 
trate-based black powders can produce residues 
with the same composition should not be a prac¬ 
tical problem in determining the type of explosive 
used if the nature of the explosion can be inferred 
from the damage, fragmentation, etc. If the resi¬ 
due were to be dealt with in isolation, however, 
then dynamite which contains sulphur and sodium 
nitrate, and sodium nitrate-based black powder 
would have to be given equal consideration as pos¬ 
sible sources (Appendix “A” no. 11). 

(vi) Aluminum 

The predicted product of the reaction of alumi¬ 
num with oxidising agents is aluminum oxide. 
However, in only one instance (KC10 4 /A1 burned 
unconfined) was aluminum oxide identified by 
XRD in residue. In every test involving aluminum, 
regardless of the stoichiometry of the mixtures, 
unreacted aluminum was recovered (Appendix 
“A” nos. 1,6). 

(b) “Water-Gel” High Explosives 

“Water-gel” high explosives, or “cap-sensitive 
slurries” are high explosives, based on ammonium 
nitrate, which can be initiated by a blasting cap. 
Like dynamite, they are distributed in “stick” 
form, but do not contain explosive oils such as 
nitroglycerine. They may, however, contain com¬ 
ponents in common with dynamites, e.g. sodium 
nitrate and ammonium nitrate. Our studies on 
residues from dynamite showed that aqueous ex¬ 
traction yielded principally sodium salts. If the 
dynamite contained sulphur, the product was so¬ 
dium sulphate or sodium carbonate sulphate. If 
there was no sulphur in the formulation, the prod¬ 
uct was sodium carbonate accompanied by nitrite 
(Beveridge et at. (1975)). 

Thus, it was of interest to determine the reac¬ 
tion products formed by the “water-gel” high 
explosives and to determine if the “water-gel” 


55 


residues could be distinguished from dynamite 
residues. 

Two explosives produced by different manufac¬ 
turers were selected. The detailed results of the 
analyses are given in Appendix “B”. The main 
points arising from the tests are discussed for each 
explosive. 

(i) “Tovex5000-SD” 

The major components of the explosive were 
monomethylamine nitrate (MMAN), ammonium 
nitrate (NH4NO3), sodium nitrate (NaN0 3 ) and 
aluminum (Al). 

Each test explosion led to recovery of a large 
quantity of aluminum flakes. However, no unre¬ 
acted explosive (a pink aluminised gel) was recog¬ 
nised in any debris. In two of the explosions, the 
identification of MMAN by IR (Parker, (1975)) 
along with unreacted sodium nitrate, aluminum 
and a nitrite reaction product, served to identify 
the source of the residue as a “water-gel” high ex¬ 
plosive of the “Tovex” type (Appendix “B” nos. 
13 & 14). In two other explosions, the residue 
components identified were sodium, nitrate, alu¬ 
minum and, in one instance, carbonate. In case¬ 
work, this residue would have been described as 
originating from any aluminised high explosive 
containing sodium nitrate—which could include 
many slurries and “water-gels” and possibly 
some less common dynamites. 

Identification of MMAN in “Tovex” residue is 
therefore most important to narrow down the 
possible sources of the original explosive. Its very 
characteristic infrared spectrum is our preferred 
method of identification. MMAN has been recov¬ 
ered from both acetone and water extracts. Con¬ 
trary to a published report (Parker (1975)) we have 
not observed MMAN to be unstable in acetone, 
and therefore have found no reason to change 
from acetone to methanol for extraction of this 
type of explosive. This aids extraction of “un¬ 
known” residues, since the normal sequence of 
ether-acetone-water may continue to be used 
without risk of decomposing MMAN. 

(ii) ‘ ‘Po werrnex 500” 

Two “Powermex-500” compositions were 
used—one with sodium nitrate as a major compo¬ 
nent, and one which contained no significant 
amount of sodium nitrate. The other major com¬ 
ponents were ethylene glycol mononitrate 
(EGMN), calcium nitrate (Ca(N0 3 ) 2 ), ammonium 
nitrate and aluminum. 

This was our first test of an explosive containing 
calcium nitrate, a white hygroscopic solid which 


has a stable tetrahydrate form and which is readily 
soluble in acetone and water. In an extraction se¬ 
quence of ether-acetone-water it is, therefore, 
likely to be found in the acetone extract. Hence, 
acetone extracts should be screened for calcium 
ions as well as for nitrate and ammonium. 

In two test explosions of the composition con¬ 
taining both sodium and calcium nitrate, the resi¬ 
dues contained unreacted calcium nitrate in the 
acetone extract, unreacted sodium nitrate and the 
reaction product nitrite in the aqueous extract, 
and insoluble unreacted aluminum. The calcium 
nitrate and aluminum were the major indicators of 
this type of explosive and served to distinguish the 
residue from dynamite. Calcium carbonate was re¬ 
covered in the insoluble residue in one explosion, 
but environmental contamination precluded posi¬ 
tive identification of calcium carbonate as a reac¬ 
tion product (Appendix “B”, nos. 18 and 19). 

The residues from the explosives with little or 
no sodium nitrate provided interesting results. In 
one test in a room which resulted in extensive 
building product contamination (ceiling collapse), 
residue containing ammonium nitrate and alumi¬ 
num was recovered from the crater. No other 
components or reaction products were identified, 
in part because of the wide distribution of cal¬ 
cium-containing building products. This was the 
only test in which any ammonium nitrate was re¬ 
covered (Appendix “B”, no. 21). A second test, in 
which residues were collected on steel, yielded a 
trace of unreacted nitrate (spot test only) by sol¬ 
vent extraction. The bulk of the residue was an in¬ 
soluble white solid reaction product and unreacted 
aluminum. The white solid consisted primarily of 
calcium and aluminum, and the precise formula¬ 
tion has yet to be determined (Appendix “B” no. 
22 ). 

No such reaction product has previously been 
recovered from dynamite or “water-gel” high 
explosives. This test underlines that reaction prod¬ 
ucts from explosives are not necessarily water 
soluble and re-emphasises the need for systematic 
analysis of residues using a variety of techniques 
both for recovery and for identification. 

SUMMARY 

The reaction products and unreacted compo¬ 
nents from burning of “home-made” explosive 
chemical mixtures and from explosion of commer¬ 
cial “water-gel” high explosives have been identi¬ 
fied and discussed. The scheme used for sys¬ 
tematic analysis has given satisfactory results for 
residues from these types of explosives. 


56 


APPENDIX “A” 

(a) Perchlorates and Chlorates 

MIXTURE 


(Weight ratio) 

1. KCIO 4 /AI 

( 2 : 1 ) 

2. KC10 4 /sucrose 

(3:1) 

3. KCIO 3 /sucrose 

(1:1) and (3:1) 

4. NaC10 3 /sucrose 

(3:1) 

5. KCIO 3 /S 


(UNCONFINED 
BURNING) 
KCIO 4 , A1 
KCl,C10f , ai 2 o 3 
KCIO 4 , sucrose 
KC1, ClOf 
glucose, fructose 
KC10 3 

kci,co^/hco 3 _ * 

NaC10 3 , 

NaCl, C0 3 _ /HCOf * 
KC10 3 , S 
KC1, K 2 S0 4 
KC10 3 , Al 
KC1 


RESIDUE 

(CONFINED 
BURNING) 
KCIO4, Al 
KC1, Cl Of 
KCIO4, sucrose 

Kci.ciof 

not tested 

sucrose 
NaCl 
KC10 3 
KC1, K 2 S0 4 
KC10 3 , Al 
KC1 


(2.5:1) 

6 . KC10 3 /A1 
( 2 : 1 ) 

Effervescence with dilute acid. 


Analysis of Residues from Perchlorates and Chlorates 


RESIDUE 


(UNCONFINED 

BURNING) 

khco 3 , kno 2 


(CONFINED 
BURNING) 
not tested 


APPENDIX "A” 
(b) Nitrates 

MIXTURE 

(Weight ratio) 

7. KN0 3 /sucrose 

( 1 : 1 ) 

8 . KN0 3 /sucrose 

( 1 : 1 ) 

9. Ca(N0 3 ) 2 /Al 

(1.5:1) 

10 . kno 3 /s/c 

(commercial) 

11 . NaN0 3 /S/C 

(7.5:1.5:1.0) 


K 2 C0 3 . 1.5 H 2 0 
NOf, NOf 
no reaction 

kno 3 

k 2 so 4 , kno 2 

(i) NaN0 3 , C0 3 _ 
Na 2 S0 4 , NaN0 2 
(residue recovered 

(ii) NaN0 3 ,NaN0 2 


sucrose 

NOf, C0 3 ~ /HCOf 
no reaction 

NOf 

K 2 S0 4 , NOf 
not tested 


by scraping) 


(NA 2 C0 3 ) N (Na 2 S0 4 ) ( ,_ n) (N = 0.2 to 0.5) 
(residue recovered by aqueous extraction) 


* Effervescence with dilute acid 


Analysis of Residues from Nitrates 


APPENDIX “B” 

Explosive 

12. Tovex5000SD 

13. Tovex5000SD 

14. Tovex5000SD 

15. Tovex 5000 SD 

16. Tovex 5000 SD 

17. Powermex 500 

18. Powermex 500 

19. Powermex 500 

20. Powermex 500 

21. Powermex 500 

22. Powermex 500 


Residue-bearing surface 

unreacted explosive 
metal 

paper, wood 

rags, wood 
metal, wood 
unreacted explosive 
rags, wood 
wood, metal, sand 
unreacted 

wood, building products 
metal 


Components Identified 

MMAN, NH 4 N0 3 , NaN0 3 , Al 
MMAN, NOf , NaN0 3 , Al 
MMAN, NH 4 +, NOf, Na, Al 
C0 3 _ /HCOf *. 

NaN0 3 , Al 

Na, Al, C0 3 - , NOf , NOf 

EGMN, Ca(N0 3 ) 2 , NH 4 N0 3 ,NaN0 3) Al 

Ca, NOf , Na N0 3 , C0 3 _ , Al 

Ca, NOf, Na, CO^“, NOf, Al, CaC0 3 

EGMN, Ca(N0 3 ) 2 , NH 4 N0 3 Al 

NH 4 + , NOf , C0 3 ~/HCOf *, Al 

NOf, Ca, Al 


* Effervescence with dilute acid 


Analysis of Residues from “Water-Gel” Explosives 


57 


REFERENCES 

Beveridge, A. D., (1978). Some Applications of 
an Analytical Data Base to the Forensic Exam¬ 
ination of Explosives Residues, Proceedings of 
the New Concepts Symposium and Workshop 
on Detection and Identification of Explosives, 
PP 559-605 NTIS, Springfield, Va. 


Beveridge, A. D., Payton, S. F., Audette, R. J., 
Lambertus, A. J., and Shaddick, R. C. (1975). 
Systematic Analysis of Explosive Residues, J. 
For. Sci. 20: 431-454 

Parker, R. G. (1975). Analysis of Explosives and 
Explosive Residues. Part 3: Monomethylamine 
Nitrate, J. For. Sci. 20: pp. 257-260. 


58 


IDENTIFICATION AND TRACING OF 
NON-EXPLOSIVE COMPONENTS IN EXPLOSIONS 


Harold R. Messier 
Chief Criminalist 
Metropolitan Police Laboratory 
St. Louis, Mo. 63103 


ABSTRACT. Non explosive components retrieved from bomb scenes frequently 
can be of value in determining the type of explosive device used. Additionally in¬ 
formation may be gained to characterize these components for tracing possible ori¬ 
gins. Methods of analysis for these components are those frequently utilized in for¬ 
ensic laboratories. Examples given will include microscopic examinations, X-ray 
fluorescence, infrared and pyrolysis G.C. 


Non-explosive components retrieved from 
bomb scenes frequently can be of value in deter¬ 
mining the type of explosive device used. Addi¬ 
tionally, information may be gained to character¬ 
ize these components for tracing possible origins. 

Methods of analysis for these components are 
those frequently utilized in forensic science labo¬ 
ratories. Primarily (1) morphological examina¬ 
tion, macro and microscopically, (2) inorganic 
analysis, X-ray fluorescence, AA, etc., (3) organ¬ 
ic analysis, infrared spectrophotometry and pyro¬ 
lysis gas chromatography. 

Explosives frequently tax the investigative agen¬ 
cies and frustrate the law enforcement commu¬ 
nity. Records indicate that little was gained from 
post explosion debris in the past to warrant suc¬ 
cessful prosecution of the guilty parties. It is this 
reason that bombings have been used as a method 
of choice. In the past several years, St. Louis has 
had a rash of auto bombings as evidenced by nine¬ 
teen injuries from auto blasts since 1970, eleven of 
which were fatal. Through the concerted effort of 
the local, state and federal government agencies 
we are beginning to see a phoenix rising from the 
ashes. Evidence of this can be seen in the success¬ 
ful prosecution in 1981 of a local dentist in a mur¬ 
der for profit scheme of the bombing death of a 
dental assistant and the conspiracy conviction of 
one in 1982 for a revenge bomb maiming of an al¬ 
leged underworld enforcer. The later victim pres¬ 
ently awaits trial for the 1980 bombing death of a 
reputed head of a Syrian faction. Investigations 
also lead to a plea of three life sentences in the 
bombing death of a teenager and his mother from 


a device sent through United Parcel. 

We have concentrated our resources in the past 
on the questions: What was the explosive? How 
big was it? etc. Why not ask first, Where did it 
come from? What type of package was it in? How 
did they place it? What makes the components 
unique? 

Items frequently recovered consist of blasting 
cap leg wires, batteries, clock parts, tape, wood, 
paper, alligator clips, etc. These are articles used 
to contain or initiate the explosion and pieces of 
them usually survive the blast. Leg wires appear as 
single stranded copper or nickel wire, 18-22 gauge 
and plastic coated. The plastic is color coded and 
tables exist for looking up the manufacturer. Plas¬ 
tic coated copper wire, having the appearance of 
leg wire but with a multi-stranded core, is used as 
antenna wire for radio controlled devices. These 
devices, readily available through hobby shops, 
are gaining in popularity for triggering explosives. 
The antenna wires are color coded from one man¬ 
ufacturer (Leisure Dynamics) to indicate the fre¬ 
quency of operation, i.e. purple receives on 72.320 
mHz. Hobby shops should not be over-looked 
when attempting to locate the origins of compo¬ 
nents and occasional visits will keep the investiga¬ 
tor up to date on many items. The ability to recog¬ 
nize items in an isolated or mangled condition is 
quite beneficial as shown in these two examples: 

CASE 1 

While processing the scene of a house bombing 
with two fatalities, an ATF agent immediately rec- 


59 


ognized a small metallic disc about the size of a 
quarter as being a glow plug used in model air¬ 
planes. It had been used as the ignition source in a 
pipe bomb. The glow plug, manufactured by Cox, 
was a high performance .049". Current was sup¬ 
plied with two 1.5 volt hobby batteries and casings 
to these were recovered. Pieces of a cardboard box 
remained with lettering from International Shoe 
Co. Checking a code number on the cardboard 
with the company, revealed that it was a discon¬ 
tinued size and no longer available. A shipping la¬ 
bel could be pieced together that had typewriting 
on it. Pieces of green colored perforated pipe strap 
were found in the debris. An examination of the 
pipe strap revealed that the edges of the perfora¬ 
tions were not green, therefore the perforations 
were stamped out of green stock and the color was 
not a product of the bombmaker. This strap mate¬ 
rial was traced to a local manufacturer, Western 
Wire, that made it from scraps of the manufactur¬ 
ing of green galvanized trash cans. The pipe strap 
was sold exclusively to Central Hardware stores at 
the time. 

After several months, a suspect was developed 
who worked at a TV repair shop. Present in the 
shop was several of the discontinued cardboard 
boxes with the International Shoe logo. Upon fur¬ 
ther questioning, the suspect confessed and de¬ 
scribed how he built the bomb. The tripping mech¬ 
anism was a toggle switch from a TV. Monofila¬ 
ment fishing line from the toggle to the box top 
flap caused the switch to throw when the lid was 
lifted. Two glow plugs were placed equidistant 
from the ends, inside of a 2"xl2" pipe, filled with 
smokeless gunpowder. A small plastic bag of 
black gunpowder surrounded each glow plug. 

CASE 2 

A dental assistant was killed when a bomb 
placed under the driver’s side nearly cut the car in 
half. A bomb scene investigator recognized frag¬ 
ments of wood and metal taped together as closely 
resembling a pressure sensitive triggering device. 
The previous device was found outside the vic¬ 
tim’s garage eight months prior. It appeared in 
this earlier attempt that the bomb partially deto¬ 
nated while trying to gain entry to the garage. The 
dynamite evidently was defective and was scat¬ 
tered around the yard. Investigations and court 
authorized wiretaps developed sufficient informa¬ 
tion to implicate a suspect with the earlier attempt. 
It became important to show a similarity beiween 


the two devices. 

After receiving all of the pieces from the fatal 
bombing that appeared to be part of the switch, 
our laboratory began reconstruction of the device. 
Even though no common parts were used in the 
two triggering systems their construction was sur¬ 
prisingly similar. Both devices were made of black 
dyed balsa wood, wrapped on the ends with black 
electrical tape. Copper appliance wire soldered to 
brass strips made contact when the auto tire rolled 
over the trigger. 

Besides the similarities in physical appearance, 
the following laboratory results were shown. In an 
attempt to reproduce the black color, balsa wood 
was treated with Magic Marker, Kiwi shoe polish 
and Higgings India Ink. Organic solubilities elim¬ 
inated the Magic Marker. X-ray fluorescence of 
the samples showed a trace of mercury in both of 
the triggering devices and in the sample of Kiwi 
shoe polish. The Kiwi Co. eventually disclosed 
that their company does add mercury to their 
formulations as a fungicide. We did not identify 
the black dye on the devices but they both had the 
same ratio of mercury levels as that found in the 
shoe polish. 

A microscopic examination of the solder re¬ 
vealed that it had been melted with something hot 
enough to melt the ends of the multi-stranded 
copper wire, probably a torch. An elemental pro¬ 
file was performed by bulk mode X-ray Fluores¬ 
cence (XRF). In an attempt to select peaks of close 
intensity for ratioing the Tin Ka and the Pb Fa were 
selected. Analysis of both devices revealed a tin 
content of 50% in each. 

The comparison revealed that even though the 
parts had a different origin the technology and the 
expertise in the design and construction of the two 
triggering devices was the same. This information 
was used in the successful prosecution of a local 
dentist in what turned out to be a murder for prof¬ 
it scheme. 

CONCLUSION 

This is only two examples where non-explosive 
components retrieved from the blast site helped to 
understand the mechanism of the device and to 
bring these cases to a successful conclusion. A 
concerted effort must be made to gain as much in¬ 
formation as possible out of the device parts. A 
well trained trace evidence analyst, working with 
the explosive residue analyst, is a great comple¬ 
ment. 


60 



Figure 1. Comparison of triggering device from bombing at¬ 
tempt (top) and reconstructed device from fatal blast (bottom). 



Figure 2. Solder examination of fatal blast (top) and attempt 
(bottom). 


BLACK WOOD 



Figure 3. X-ray fluorescence (XRF) of black dyed wood trig¬ 
ger showing traces of mercury. 



Figure 5. XRF of Solder on trigger device. S K /pb L ratio is 
0.34. 





Figure 6. Glow plug used in model airplanes found at scene of 
blast fatal to two. This was the source of ignition in a pipe 
bomb. Note size in comparison to screw. 


61 













































Figure 7. Debries found in house blast fatal to two. Items that 
can be seen are (1) 1 Vi volt hobby battery, (2) green pipe strap 
(3) cardboard box. 


62 










EXPLOSIVE ANALYSIS KIT 


Lyle Malotky and Steven Downes 
Naval Explosive Ordnance Disposal Technology Center, 
Indian Head, MD 20640 


ABSTRACT. An explosive analysis kit was developed to perform the timely field 
separation and identification of 28 different explosives and energetic materials. 
The kit uses solubility and thin-layer chromatography (TLC) to separate mixed ex¬ 
plosives and identify each explosive component. The kit, with sufficient materials 
to perform ten analyses, is packaged in a briefcase. The solvents for sample disso¬ 
lution and TLC separation are packaged in single-use lead tubes to insure compo¬ 
sition and lack of contamination. The kit is assembled from commercial compo¬ 
nents, with custom packaging required for filling and sealing the lead solvent 
tubes. A battery-operated ultraviolet (UV) light visualizes the TLC plates, elimi¬ 
nating the need for corrosive reagents and ambiguous color-forming reactions. A 
worksheet, provided with the instructions, guides the operator through the analysis 
and is used to record data and help make the identification. The kit identifies the 
components of booster and main charge explosives, as well as selected oxidizers, 
propellants, and other energetic materials. After limited training, 62 U.S. Marine 
Corps EOD technicians tested the kit. Their performance was good, and their reac¬ 
tion to the kit was very favorable. 


INTRODUCTION 

The Naval Explosive Ordnance Disposal Tech¬ 
nology Center (NAVEODTECHCEN) is respon¬ 
sible for the research and development of special¬ 
ized equipment, techniques, and procedures re¬ 
quired to support operational explosive ordnance 
disposal (EOD) units in the location, neutraliza¬ 
tion, and disposal of surface and underwater ex¬ 
plosive ordnance. This Joint-Service program en¬ 
compasses all current and obsolete explosive ord¬ 
nance (both domestic and foreign), including im¬ 
provised explosive and nuclear devices that may be 


employed by dissident and terrorist groups. 
NAVEODTECHCEN also provides significant 
support to activities concerned with the demilitari¬ 
zation of chemical weapons and the reclamation 
of ordnance-contaminated land and water areas. 
Finally, support is provided to the Federal Bureau 
of Investigation, the Secret Service, civilian law 
enforcement agencies, and other government de¬ 
partments. 

In response to a Marine Corps requirement, an 
explosive analysis kit was developed to allow EOD 
technicians to identify in the field 28 explosives 
and energetic materials (see Table 1). 


Table 1. LIST OF EXPLOSIVES AND ENERGETIC MATERIALS 



Special purpose 

Energetic 

Pyrotechnic 

Common explosives 

explosives 

plasticizers 

ingredients 

TNT 

TNB 

FEFO 

Potassium 

Nitroglycerin 

DATB 

TEGDN 

chlorate 

Tetryl 

DIPAM 

2,4 DNT 

Barium nitrite 

RDX 

HNS 

MTN 

Ammonium 

HMX 

TATB 

BDNPA 

perchlorate 

HND 

R-salt 

BDNPF 


PETN 

BTNEU 



Ammonium picrate 

BTNEN 




Picric acid 
Nitrocellulose 
Ammonium nitrate 


63 


This kit was developed at the Naval Surface 
Weapons Center, White Oak, Maryland, where 
scientists were given a list of explosives to be iden¬ 
tified and general guidelines. The analysis system 
they recommended employed both solubility 
measurement and thin-layer chromatography 
(TLC) to identify the explosives (see NSWC TR 
79-455). The kit consists of a carrying case, reuse- 
able components, and enough single-use compo¬ 
nents for ten analyses. Currently packaged in a 
briefcase, the kit weighs 5.9 kilograms (13.0 
pounds) and occupies 0.014 cubic meter (0.5 cubic 
foot) of space. The cost of a prototype kit capable 
of performing ten analyses is estimated to be 
$1,000, with approximately half that cost for re- 
useable components. It is anticipated that refills 
for the single-use components will be fielded as a 
ten pack containing all single-use components, 
plus low-cost multiuse components and analysis 
worksheets. 

Operational suitability of the kit was demon¬ 
strated using the personnel of the EOD units at 
Twenty Nine Palms and Camp Pendleton, Cali¬ 
fornia, and at Beaufort Air Station, South Caro¬ 
lina, and Camp Lejeune, North Carolina. The 
personnel were trained, divided into teams, and al¬ 
lowed to proceed at their own pace. The teams 
were given unknown explosives, serialized work¬ 
sheets, and a questionnaire to be completed after 
the evaluation. 

DESCRIPTION 

The reagents to perform the solubility measure¬ 
ment and TLC tests are packaged in single-use 
tubes. The solvents for the TLC separation are 
mixed with about 6-percent Cab-O-Sil, a finely 
divided silica, to form a gel the consistency of 
toothpaste. This gel allows the solvent to be han¬ 
dled as a solid. Fielding single-use tubes insures 
the user that the proper solvent mixtures are in¬ 
stantly available. The tubes are color coded red, 
white, and blue for identification. Upper storage 
and use temperature has been set at 50 °C (122°F) 
because the boiling point of acetone, which is used 
for explosive dissolution, is 56°C (133 °F). 

Three simultaneous TLC separations are per¬ 
formed using three different hexane ethyl acetate 
solvent mixtures. In thin layer chromatography, a 
solvent or mixture of solvents proceeds by capil¬ 
lary action up a plate covered with a thin layer of 
silica gel or other high-surface-active area mate¬ 
rials. The material to be separated is not only car¬ 
ried along with the solvent but is also absorbed by 


the silica gel. The time a component spends in the 
solvent versus the time it spends in the gel deter¬ 
mines how far up the plate it travels. The relative 
distance the sample travels is expressed as a ratio 
of the distance the sample travels divided by the 
distance the solvent travels. The ratio, commonly 
called the RF value, should ideally be constant; 
however, it is affected by changes in solvent com¬ 
position, the degree of sample loading, the activity 
of the TLC plate, etc. For this reason, a reference 
sample mixture has been included in the explosive 
anlaysis kit. The reference sample is a mixture of 
the explosives TNT, picric acid, RDX, and tetryl. 
The quantity contained, about 16 milligrams per 
sample, is small enough to be exempt from Navy 
Explosive Safety Stowage and DOT Hazardous 
Materials regulations. 

The silica gel on the TLC plate contains dye 
which fluoresces orange when excited with 
short-wave-length (254 nm) ultraviolet (UV) 
light. A majority of explosives absorb strongly in 
this region of the spectrum and show up as dark 
spots on an orange background when the TLC 
plate is interrogated with the UV light. 

USE OF THE KIT 

The analysis of an unknown explosive or mix¬ 
ture of explosives can be broken into four major 
steps: preparation, separation, visualization, and 
identification. The use of the kit will be illustrated 
by a typical analysis. 

A spatula and alien-head bolt are used to meas¬ 
ure about 100 milligrams of explosive into each of 
two vials. One milliliter of water is added to one 
vial, and 1 milliliter of acetone is added from a 
lead tube to the other vial. One milliliter of ace¬ 
tone is also added to the reference sample. The 
samples are allowed to dissolve. The extent of so¬ 
lution and appearance is noted on the worksheet. 

Using disposable 1-microliter pipettes, 

1-microliter spots of each solution are placed on 
each of three 2-by-7 centimeter TLC plates. The 
plates are placed in plastic developing chambers 
charged with solvent gel of three hexane ethyl ace¬ 
tate mixtures. The mixtures’ compositions (6:1, 
3:1, and 1:3) provide a range of polarity capable 
of separating the explosives of interest. About 5 
minutes is required for the solvent to proceed up 
each TLC plate, then the plates are removed, la¬ 
beled, and allowed to dry. 

Each TLC plate is viewed or visualized by the 
UV light. The silica gel fluoresces orange, but the 
UV light is absorbed by the explosives, resulting in 


64 


a gray, nonfluorescing spot on the plate. The posi¬ 
tion of the separated explosives is marked on the 
plates and the distance the explosive traveled rela¬ 
tive to the solvent is calculated. The reference 
sample has been included to increase the analyst’s 
confidence in the procedure as well as show where 
the frequently encountered explosives, TNT, 
tetryl, RDX, and picric acid, are encountered. 

Identification of the unknown is based on all in¬ 
formation available to the analyst: RF value, ex¬ 
plosive and photo-oxidation color, solubility, and 
origin. Identification by this field system is not un¬ 
equivocal; similar explosives (i.e., RDX and 
HMX) may differ only slightly; therefore, all clues 
must be used. Mixed explosives will produce sever¬ 
al spots on the TLC plate—one from each explo¬ 
sive. Aluminized explosives will be indicated by a 
gray, undissolved residue. 

OPERATIONAL TESTS 

Operational tests were conducted using Marine 
Corps EOD technicians to determine if the kit 
could be reliably operated, to identify any resolva¬ 
ble shortfalls in the kit, and to determine the ap¬ 
propriate training and practice levels. The testing 
was conducted in two series, preliminary tests in 
the spring of 1980 in California, followed by addi¬ 
tional tests in the spring of 1981 in North and 
South Carolina. Between these two series of tests, 
the instructions were modified to correct deficien¬ 
cies revealed, and the rechargeable battery-oper¬ 
ated UV light was replaced by a larger lan¬ 


tern-battery-powered unit. 

A total of 62 technicians working in teams used 
the kit to perform analyses on 87 unknowns. Dur¬ 
ing the testing, 20 different unknowns were used, 
five of which contained two different major ingre¬ 
dients, for example, pentolite which contains TNT 
and PETN. Of the analyses, 72 percent were total¬ 
ly correct. The incorrect analyses tended to be one 
explosive identified as a similar explosive. The 
conclusion reached was that the options facing the 
analyst were too great. In the kit planned for field¬ 
ing, most or all of the energetic plasticizers and 
special-purpose explosives will be dropped, reduc¬ 
ing the identification options available to the oper¬ 
ator. 

CONCLUSIONS 

Results of the testing demonstrate that the ex¬ 
plosive analysis kit allows the field identification 
of various explosives and energetic ingredients by 
nonscientific personnel. 

The Marine Corps EOD technicians evaluating 
the kit reacted very favorably and achieved a cor¬ 
rect analysis rate of 72 percent. 

Deficiencies of the kit that resulted in false iden¬ 
tification or missed components have been identi¬ 
fied. Proposed corrective actions include: reduc¬ 
ing the number of options by eliminating those ex¬ 
plosives not frequently encountered, providing 
more extensive training to the personnel before the 
actual performance of the test, and cataloging ex¬ 
plosives by their usual application. 


65 




















* 












































































ORGANIC SOLVENT EXTRACTS OF EXPLOSIVE DEBRIS: 
CLEAN-UP PROCEDURES USING BONDED PHASE SORBENTS 


Richard A. Strobel, Richard E. Tontarski, 
Forensic Chemists, Forensic Science Branch, 
Bureau of Alcohol, Tobacco and Firearms, 
1401 Research Blvd., Rockville, MD 20850 


ABSTRACT. A number of sensitive techniques exist today for the detection of 
explosives. However all their sensitivity and specificity may be lost when “dirty” 
or “real world” samples are subjected to analysis. Improved chromatographic 
techniques and sensitive detectors have aided the situation. Unfortunately, many 
of the “real world” samples encountered contain a complex mixture of interfering 
substances. The chromatography systems can not adequately separate the explo¬ 
sives of interest from these contaminants. These “dirty” samples require a 
pre-treatment prior to being subjected to chromatography and detection. The use 
of porous polymers and bonded phase adsorbants as a clean-up procedure is ex¬ 
plored in this work. Retention properties of both explosives and contaminants are 
studied, and an analytical scheme is presented which optimizes the separation of 
the explosive from the contaminants. 


INTRODUCTION 

The identification of high explosives (TNT, 
RDX, Tetryl and PETN) in post-blast debris 
usually involves extracting the debris with a suit¬ 
able solvent such as acetone or methanol and ana¬ 
lyzing the extract by chromatography coupled 
with a detection technique. Many of the tech¬ 
niques, such as Thin Layer Chromatography 
(TLC), High Performance Liquid Chromatog¬ 
raphy/Mass Spectroscopy (HPLC/MS), Gas 
Chromatography/Mass Spectroscopy (GC/MS) 
or HPLC/UV allow detection at the nanogram 
and picogram levels. However, contaminants ex¬ 
tracted from the debris with the explosive of in¬ 
terest often make these sensitive detection tech¬ 
niques useless. 

Many times “dirty” samples contain greater 
quantities of contaminants than they do explo¬ 
sives. The sample to be analyzed is, therefore, 
often composed of a small amount of explosive in 
a large quantity of a complex, dirty matrix. Expe¬ 
rience has shown that chromatographic techniques 
(TLC, HPLC and GC) alone are not sufficient to 
separate the explosive from the contaminants, and 
provide clean samples to the detectors. As a result, 
detectors often respond to the contaminants, 
masking the detection of the explosive of interest. 


This contamination problem initiated work on 
clean-up procedures. 

Our initial work examined the use of Rohm and 
Haas AMBERLITE XAD resins to clean up ex¬ 
plosive residue extracts. We found that XAD-2 
(cross-linked styrene divinylbenzene porous poly¬ 
mer) and XAD-7 (porous polymer with an alkyl 
ester functional group) resins retained and eluted 
explosives from various aqueous solvent systems 
with high recovery rates. Unfortunately they also 
retained and eluted many of the contaminants in 
the sample matrix. In an effort to attain a greater 
selectivity a series of bonded phase sorbents was 
examined. 

MATERIALS 

The sorbents were obtained from Analytichem 
International, and are known as their BOND 
ELUT (TM) system. The system consists of col¬ 
umns which are available with 18 different bonded 
phases. The column packing is silica gel which has 
a monofunctional chemical moiety attached. 
Those phases evaluated are shown in Table 1. The 
bonded phases tested were selected because their 
functional groups were expected to be effective in 
selectively retaining explosives from various solu¬ 
tions. 


67 


Table 1. BONDED PHASES TESTED FOR RETENTION OF EXPLOSIVES 

Bonded Phases Tested 

Analytichem Bond Elut (TM) Columns 
Column volume: 2.8 ml 
Sorbent mass: 500 mg. 

Non-Polar Polar 

Cl 8 Octadecyl CN Cyanopropyl 

C8 Octyl 20H Diol 

C2 Ethyl 

PH Phenyl 

CH Cyclohexyl 


In theory, a high degree of selectivity toward the 
explosive should be possible by taking advantage 
of the interaction of the isolate (explosive) with 
the bonded phases and the solvents used (which 
change when extracting debris, depositing the 
sample on the column or eluting the isolates). 

A standard explosive mixture (SEM) which in¬ 
cluded RDX, TNT, Tetryl, and PETN at 10 PPM 
concentrations in acetone was used throughout the 
study. The samples were placed on the columns by 
aspirating the sample, in a suitable solvent, 
through the column. Samples were eluted with two 
500 ul washes of solvent placed on the top of the 
column. The column was then centrifuged with 
the sample and eluent passing into a suitable re¬ 
ceiver (13 x 100 mm culture tubes). Columns were 
conditioned prior to use according to manufactur¬ 
er’s instructions. 

A Waters Model 6000A HPLC pump using a 
Radial-PAK C-18 column with the Radial Com¬ 
pression Module and Waters Model 441 UV detec¬ 
tor set at 214 nm was used to measure quantities of 
explosives recovered. The mobile phase was aceto- 
nitrile:water 70:30 run isocratically with a 1.0 
ml/minute flow rate. 

COLUMN EVALUATION—RETENTION 
OF EXPLOSIVES 

The first step in evaluating each bonded phase 
was to measure its effectiveness in retaining and 
subsequently eluting the explosives. The non-polar 
phases were examined first. These phases function 
by retaining hydrophobic organic compounds 
from reverse phase solvent systems. Since explo¬ 
sives are separated from debris using polar sol¬ 
vents ( e.g . acetone or methanol) it was necessary 
to convert the solvent containing the explosive to 
an aqueous system in order to promote retention 
of the explosive on the column. A 10 fold volume 
of deionized water was added to the SEM. This 1 
ml acetone/10 ml water solution containing 10 ug 
of each explosive was then passed through the 
non-polar column with vacuum. 


The columns were then eluted with 0.5 ml of 
70:30 acetonitrile:water and analyzed by 
HPCL/UV using peak areas to determine the 
quantity of explosive retained and recovered. 

Of the columns evaluated only the CH, C18 and 
PH bonded phases showed good retention (better 
than 95% recoveries) from the acetone/water. 

The polar columns, CN and DIOL, which were 
also reported to retain materials from the reverse 
phase were similarly evaluated. Testing showed 
that they were not effective in retaining explosives 
from acetone/water mixtures. 

Although the polar columns were not effective 
in a reverse phase system their use with a non¬ 
polar solvent system needed to be evaluated. 
Methylene chloride (CH2CL2) was chosen as a 
solvent since the explosives of interest are soluble 
in it. A 10 PPM mixture of the same explosives in 
CH2CL2 was prepared. Hexane was added to the 
CH2CL2 explosive mixture (1:1) to make the sys¬ 
tem more non-polar and to promote the retention 
of the explosives on the polar CN and DIOL col¬ 
umns. The explosives were then eluted with 0.5 ml 
of 70:30 acetonitrile:water and anayzed by 
HPLC/UV, as was done previously. The CN col¬ 
umn proved to be more efficient than the DIOL 
column in the recovery of TNT and PETN. Re¬ 
coveries for the other explosives were approxi¬ 
mately equal (95% recoveries or better) on both 
columns. 

RESULTS AND DISCUSSION 

The results of the column evaluation are sum¬ 
marized in Table 2. These results led to the estab¬ 
lishment of the analysis scheme in Figures 1 and 2. 
Samples are first placed on the column in a solvent 
(acetone) to which 10 parts of water have been 
added. Once the explosives have been retained, the 
columns can be washed with a 20:80 acetoni- 
trile:water mixture (2 column volumes) to remove 
polar contaminants. The CH column was chosen 
because of high recoveries and it’s superior selec¬ 
tivity compared to the C18 column. The CH col- 


68 


Table 2. COLUMN EVALUATION STUDY. SUMMARY OF RESULTS. 


Columns 

C18,CH,PH 

CN 

C2;C8 

DIOL 


Explosives 

Extracted 


Eluting 

Solvents 


Cleaning 

Solvents* 


From aqueous 
system A 


70:30 CH3CN:H z O or 20:80 

1:1 CH2CL2:Hexane CH3CN:H 2 0 


From non-polar 70:30 CH3CN:H 2 0 Hexane 

NOT EFFICIENT IN RETAINING EXPLOSIVES FROM SYSTEM A 
NOT EFFICIENT IN RETAINING TNT, PETN FROM SYSTEM B 


Contaminant 

Removed 

Polar 

Non-polar 


SYSTEM 

A 10:1 H 2 0:ACETONE—Polar System 

B 1:1 CH2CL2:HEXANE—Non-Polar System 

♦Solvent which could be used to rinse the column containing the explosives without eluting the explosives. These are only two of nu¬ 
merous solvents, or solvent combinations, which need to be examined. 


umn is then placed on the CN column by means of 
an adaptor and the explosive is eluted using a mix¬ 
ture of methylene chloride:hexane 1:1. As seen 
from previous column evaluation, the explosive 
will now be retained on the polar CN column. 
Column afterwash studies had shown that the 
CH2CL2:hexane completely eluted the explosives 
from the CH column with two 0.5 ml washes. The 
CN column can now be washed with hexane to re¬ 
move non-polar contaminants (two column vol¬ 
umes). The final elution of the explosive from the 
column is accomplished using the HPLC mobile 
phase (acetonitrile:water 70:30). The mobile phase 
(0.5 ml) is placed on the column and centrifuged 
through the column into a suitable container (13 x 
100 mm culture tube). The sample is then ready 
for HPLC analysis. Results of recovery studies us¬ 


ing this procedures for the SEM is shown in Table 
3. 


TABLE 3. Recovery study results for various explosives. 


10 PPM of the SEM was placed on the CH column from an 
acetone:H20 solution. The column was then eluted with 
CH2CL2:hexane (1:1) onto a CN column. The explosives were 
eluted with the HPLC mobile phase. 


Explosive 

Percent Recovery 

HMX 

24 % a 

RDX 

99% 

TNT 

94% 

Tetryl 

96% 

PETN 

95% 

The poor recovery for HMX was a result of attempts to 

optimize the cleanup 

procedure for the five commonly 

encountered explosives. 

HMX can be recovered with great- 


er efficiency by changing various procedural parameters. 


SAMPLE ON COLUMN 


WASH 


ACETONE/HOH 1:10 



P 

WASTE 


4 

NON-POLAR COLUMN 
CH 


CH3CN/HOH 20:80 



P 

WASTE 


E - EXPLOSIVES 

P - POLAR CONTAMINANTS 

N - NON-POLAR CONTAMINANTS 



Figure 1. (A) Explosives are extracted from the acetone/H 2 0 solution and trapped on the CH column. (B) Cleansing solvents can 
then be used to further remove polar contaminants. 


69 





CH2CL2/HEXANE 


ELUTION 


NON-POLAR 

COLUMN 



UMN 


WASTE 



N 

WASTE 


ELUTION 


CH3CN/HOH 70:30 



E 

HPLC 

ANALYSIS 


Figure 2. (C) The explosives are eluted from the CH column and trapped on the CN column. (D) The CN column can then be 
washed with cleansing solvents. (E) Explosives are then eluted with the HPLC mobile phase for analysis. 


This procedure makes use of the dual character 
of the explosives examined which may allow inter¬ 
fering materials extracted with them to be re¬ 
moved prior to analysis. The explosive molecules 
have both a large non-polar hydrocarbon portion 
to their structure as well as a polar portion. These 
properties allow the molecules to be retained on a 
non-polar column from a polar solvent system 
while allowing the polar contaminants to pass 
through. The explosives can then be eluted with a 
moderately non-polar solvent system onto a polar 
column. As the explosives are retained on the 
polar column, non-polar contaminants pass 
through as waste. 

Additional Sample Clean-up 

After application, the explosives are attached to 
the bonded phase of the column. This mechanism 
will allow for additional clean-up of the sample 
prior to analysis. When bound to the non-polar 
phase, polar cleansing solvents should remove 
additional polar contaminants. When bound to a 
polar phase a non-polar cleansing solvent should 
remove additional non-polar contaminants. Table 


2 lists two cleansing solvent systems that have been 
used with minimal loss of explosives. Due to the 
complexity of real-world postblast debris, addi¬ 
tional work on suitable cleansing solvent systems 
is needed. Since blast debris varies from case to 
case the retention properties of the contaminants 
to the bonded phases also needs further study. 

CONCLUSION 

Organic explosives can be retained on bonded 
phase sorbents utilizing the explosive molecule’s 
ambivalent character. Both polar and non-polar 
sorbents work well for retaining the explosives 
studied. Virtually complete recovery can be ob¬ 
tained through the procedure. The sorbent proper¬ 
ties of the bonded phase columns lend themselves 
to pre-analysis sample clean-up. 

ACKNOWLEDGEMENT 

We wish to thank Carl Selavka, a graduate stu¬ 
dent at Northeastern University for his assistance 
in this work. 


70 






A SCHEME FOR THE ANALYSIS OF 
EXPLOSIVES AND EXPLOSIVE RESIDUES 


Terry L. Rudolph and Edward C. Bender 
Instrumental Analysis Unit, 

FBI Laboratory, 
Washington, D.C. 20535 


ABSTRACT. The FBI Laboratory has developed a new scheme for the analysis 
of explosive residues. This scheme is based on a water and/or organic solvent wash 
of bombing debris. Inasmuch as several high explosives such as dynamites and 
water gel/slurries contain both organic and inorganic species, it is often necessary 
to fully identify the explosive, to perform both washes on the debris. This scheme 
highlights the use of x-ray powder diffraction and ion chromatography (IC) for 
the analysis of the water wash. Such hard to identify inorganic species as mono- 
methylamine nitrate can easily be identified with the IC methods reported. The or¬ 
ganic solvent wash highlights the use of HPLC and GC/MS methods. HPLC 


methods utilize both normal and reverse 
wavelength and TEA detectors. 

During the past 2-3 years the FBI Laboratory 
has been involved in the investigation of hundreds 
of terrorist and other criminal bombings. These 
bombings were committed with a wide variety of 
explosives, from low explosives, such as, home¬ 
made black powder to high explosives, such as, 
water gel/slurries or military demolition explo¬ 
sives like TNT or C-4. 

Many of the high explosives, when undergoing a 
high order detonation leave little or no residue, 
making their detection very difficult. When the 
bombing is, for example, of a building, the prob¬ 
lem of detecting the explosive is compounded be¬ 
cause traces of residues left at the scene could be 
mixed with tons of building debris. 

Faced with many high explosives capable of 
leaving only traces of residues, complicated crime 
scenes, and numerous requests from state and lo¬ 
cal laboratories for the FBI Laboratory’s proced¬ 
ure for explosive analysis, the Instrumental Analy¬ 
sis Unit (IAU) of the FBI Laboratory developed a 
scheme for the analysis of explosives and explosive 
residues. It was felt that the development of a for¬ 
mal procedure or scheme utilizing the latest instru¬ 
mentation was necessary to give the explosive ana¬ 
lyst an edge when faced with some of the pre¬ 
viously mentioned problems. 

Figure 1 represents the overall scheme for explo¬ 
sive and explosive residue analysis developed by 


phase chromatography and variable UV 


the IAU of the FBI Laboratory. This scheme has 
been used very successsully for the past two years 
and has resulted in the successful analysis of hun¬ 
dreds of bombing cases and the identification of 
the explosive used. 

This paper will highlight the four main instru¬ 
mental methods noted in the scheme. X-ray pow¬ 
der diffraction (XRPD), ion chromatography 
(IC), liquid chromatography (HPLC), and gas 
chromatography/mass spectroscopy (GS/MS). 

The first step in the analyses of debris from a 
bombing is often a head space analysis. When the 
debris contains soil, small concrete fragments, 
plaster, synthetic rubber foam, cloth fragments, 

Debris From Bombing 

Head Space Analysis 

Physical Examination 

I-^ I 

Inorganic Wash Organic Wash 

Water Wash Evaporation Organic Solvent Wash 

I I 

Spot Tests Liquid Chromatography 

I I 

X-Ray Diffraction GC/Mass Spect 

I 

Elemental 

Analysis 

Ion Chromatography 

Figure 1. Scheme for the Analysis of Explosives. 


71 






or other small absorbent type material a head 
space analysis is conducted and any volatile or¬ 
ganic explosive materials usually can be removed 
and identified. 

The debris to be analyzed is placed in a one gal¬ 
lon aluminum paint can, gently heated on a hot 
plate, while the volatile vapors are removed from 
the top of the can by sucking them off with a 
vacuum. All vapors, explosive and otherwise, are 
trapped on a 1 ‘/ 2 -inch charcoal trap. The volatile 
materials are then washed off the charcoal trap 
with dichlorethane and analyzed by HPLC. The 
actual analysis will be discussed in the HPLC 
METHODS section. 

After the head space analysis, or if the debris 
would physically not permit a head space analysis, 
such as large metal fragments from a car or plane, 
the next step is a physical examination of the de¬ 
bris. This could also include a microscopic exami¬ 
nation of small metal fragments, such as, from a 
pipe bomb. 

The object of the physical examination is to de¬ 
termine if anything foreign to the debris is present 
or if anything of evidentiary value can be ob¬ 
served. Also at this time the debris is often divided 
into two parts; one part to be washed with water, 
the other with an organic solvent, such as, ace¬ 
tone. An alternate approach is to first wash the de¬ 
bris with acetone and then water. 

Although the water wash is to remove inorganic 
residues and explosives and virtually all low explo¬ 
sives are inorganic in nature; numerous high ex¬ 
plosives, such as the dynamites, water gel/slurries 
and ammonium nitrate/fuel oil mixtures also con¬ 
tain inorganics, making the water wash necessary 
for a complete high explosive analysis. 

The acetone wash is designed to remove the or¬ 
ganic explosives from the debris. Most organic 
components found in high explosives, such as, 
TNT, nitroglycerin (NG) and pentaerythritol 
tetranitrate (PETN) are relatively soluble in ace¬ 
tone and will be removed in a wash. 

Looking first at the water wash, it is conducted 
with distilled or deionized water. As small a quan¬ 
tity of water as possible should be used ie., 25-50 
ml of water, for typical pipe bomb fragments to 
150-300 ml of water for larger metal fragments. 
From this initial wash a 5-10 ml aliquot is re¬ 
moved for the IC analysis, while the rest is evapo¬ 
rated to dryness. 

The evaporate is used for spot tests and for 
XRPD analysis. Spot tests conducted routinely by 
the IAU are summarized in Table 1. 


Table 1. SPOT TEST FOR EXPLOSIVE RESIDUES 


Reagent 

1 % Silver Nitrate 
3% Barium Choride 
5% Diphenylanine 
Nitron 

Potassium Hydroxide 
Hydrochloric Acid 
Aniline Hydrochloride 


Test 

Chlorides 

Sulfates 

Oxidizing Agents (Nitrates) 

Nitrates 

Ammonium 

Carbonates 

Chlorates 


X-RAY POWDER DIFFRACTION METHODS 

XRPD is an instrumental method of analysis in 
which the intensity of X-rays diffracted from a 
crystalline specimen is recorded as a function of 
the diffraction angle. The diffraction angle or 
X-ray peak is related to the distance between cry¬ 
stal planes or “d” value. Individual “d” values 
make up the diffraction pattern for a crystalline 
substance. 

The basis of XRPD, that makes it valuable in 
explosive residue analysis is it gives a chemical fin¬ 
gerprint of each substance analyzed. Every cry¬ 
stalline material gives a characteristic X-ray pat¬ 
tern and no two chemically distinct substances 
give identical patterns. It is only necessary to 
match the pattern of an unknown substance with a 
known pattern to make an identification. 

Instrumentation 

The IAU uses Philips XRG 3000 and 3100 Gen¬ 
erators which are equipped with a Philips vertical 
diffractometer, graphite monochromator and sol¬ 
id state scintillation counter. The X-ray generator 
is operated at 45 Kv and 35 mA and yields stand¬ 
ard CuKa radiation at 1.5418 A 0 from the copper 
target X-ray tube. 

Each specimen was scanned in the 20 range 
from 60° to 0° at 1 0 per minute. The “d” values 
were searched through JCPDS search manuals us¬ 
ing the Hanawalt Method. 

Applications 

Although XRPD can be applied to explosive 
and explosive residue analysis in many different 
ways, in this work they are divided into three areas 
as follows: 1, Analysis of Post-Blast Explosive 
Residues, 2, Identification and Confirmation of 
Pre-Blast Explosives, and 3, Identification of Un¬ 
known Materials. 

Both high and low explosives can leave enough 
post-blast residues to be recovered and analyzed 
by XRPD but the high explosives are limited to 
some dynamites, water gel/slurries and some am¬ 
monium nitrate mixtures. Most of the residues re- 


72 


Wi Potassium Sulfate 
] Potassium Carbonate 


2.99 



Figure 2. XRPD of Black Powder Combustion Products. 


covered in sufficient amounts for analysis are low 
explosive combustion products. 

The most common low explosive used in impro¬ 
vised explosive devices (lED’s) today is black pow¬ 
der. Figure 2 shows the X-ray diffractogram of 
the residue from a black powder pipe bomb. Both 
potassium sulfate and potassium carbonate have 
been identified in the residue. Based on this analy¬ 
sis a determination could be made that black pow¬ 
der was the main explosive used. 

XRPD is a very powerful tool in identifying 
solid residues in post-blast situations and can be 
applied, as shown in Figure II, to mixtures. 

Another useful application of XRPD is to con¬ 
firm the identity of a known explosive in pre-blast 
situations. Figure 3 shows the diffractogram of an 
unknown explosive taken from and IED that was 
found on an airplane in Brazil. A simple interpre¬ 
tation procedure reveals the material to be PETN. 
XRPD again offers a quick and easy method of 


confirming the identity of materials known to be 
explosives. 

The last application of XRPD in explosive 
analysis is its value to identify unknown materials 
/. e ., materials taken from searches of suspects 
home or business, and those found at or near the 
bombing scene. 

ION CHROMATOGRAPHY METHODS 

Ion Chromatography is a term coined by the 
Dionex Corporation to encompass all techniques 
used for separating and quantitating both inor¬ 
ganic and organic ions, and in its broadest sense is 
the chromatography of ions. 1C combines the effi¬ 
cient separation capabilities of ion exchange resins 
with conductometric detection. Conductometric 
detection is an ideal technique to monitor ion ex¬ 
change separations because of its universal and 
linear response. 

Ion exchange resins used in IC are spherical in 



Figure 3. XRPD of PETN. 


73 



















nature composed of a polystyrene matrix 
cross-linked with divinylbenzene. Functional 
groups, such as, sulfonic acid and quaternary am¬ 
monium are chemically bonded to the matrix. 
These groups provide exchange sites where their 
counter ions are exchanged with sample ions as the 
sample flows through the resin bed. Retention 
time depends on several factors, the most notable 
are: (1) resin characteristics, (2) ion size, 
(3) ionic charge, (4) ion concentration and ionic 
composition of the mobile phase. 

Instrumentation 

The IAU uses a Dionex Ion Chromatograph 
Model 16 to perform its explosive residue analysis. 
The Model 16 is equipped with a 100 ul sample 
loop and a 6 ul flow through conductivity detector 
Figure 4 is a photograph of the Dionex Model 16. 

Since IC is a form of liquid chromatography it 
has a mobile and stationary phase. The mobile 
phase or eluent differs according to the type of 
analysis being performed. In explosive residue 
analysis there are two basic types of analysis; 
anion and cation. The eluent for standard cation 
analysis is 0.01 N HC1 in 30% methanol. 

The columns used in the standard cation analy¬ 
sis are as follows: 3 x 50 mm Dionex pre-column 
and a 6 x 200 mm Dionex cation separator column 



in series with a Dionex 9 x 150 mm cation suppres¬ 
sor column. 

In standard anion anaysis the eluent is 0.003M 
Na H C0 3 /0.0024M Na 2 C0 3 at a flow of approxi¬ 
mately 3.0 ml/min. The columns are a 3 x 50 mm 
Dionex pre-column and a 4.0 mm x 250 mm 
Dionex separator column in series with a Dionex 
anion fiber suppressor. 

Other detectors used in the analysis of explo¬ 
sives are a Dionex Electrochemical Detector with a 
2.6 ul cell and a Perkin Elmer LC-55 variable 
wavelength UV-VIS. spectrophotometer equipped 
with a 10 ul cell. Detection is measured at 210 nm. 

Figure 5 is a block diagram illustration of the IC 
set-up of the IAU. 

Basically the operation is as follows: A mixture 
of sample cations containing, for example, Na + , 
K + , and NFLC is injected into the mobile phase of 
.01 N HC1 in 30% methanol. Sulfonic acid ex¬ 
change sites in the separator column, exchanges 
H + for the Na + , K + and NFLC ions. After the ions 
are separated on the ion exchange bed they exit at 
various times from the bottom of the column in a 
background of HC1 eluent. 

The mixture then enters the second column, the 
suppressor, containing a strong base ion exchange 
resin in the OH form. Two reactions take place. 
First the background HC1 ions of the eluent are 
removed leaving deionized water. The cations are 
converted to their hydroxides in the second reac¬ 
tion and their conductivity is measured now in the 
suppressed background of water. 

Applications 

There are basically two applications of IC to ex¬ 
plosive analysis. They are as follows: (1) Trace 
analysis of post-blast explosive residues, (2) 
Identification of pre-blast explosive components. 

By far the widest application of IC in explosive 
analysis has been trace analysis of post-blast 
residues. Table 2 summarizes some of the cation 
and anions that can be analyzed by IC. 

Figures 6 and 7 show the separation of the nor¬ 
mal cations and anions, respectively, as detected 
with the conductivity detector. 


| Pump | 


Separator 

Column 


Electrochemical 

Cell 


Injection 

Port 


Suppessor 


Conductivity 

Cell 


Recorder 


| Recorder 1 | Recorder 1 - 1 UV Cell | - 1 Waste | 


Figure 4. Photograph of an Ion Chromatograph. 


Figure 5. Block Diagram of Ion Chromatrograph Set-Up. 


74 














































Table 2. IONS ANALYZED BY IC IN EXPLOSIVE RESI¬ 
DUES 


COMMON CATIONS 


I Cation Analysis 

monovalent Na + ,K ,NH 4 -l-, *MM A + 
divalent Ca+ + ,MG + + ,Ba + + ,SR+ + 

II Anion Analysis 
F-,C1-,N0 2 - Br- P0 4 -3,N0 3 - 

S 0 4 -2 CIO 3 - S-2 SCN- CN 
NOj- from CIO 3 - 


Detector System 
conductivity 
conductivity 
Detector System 
conductivity 
electrochemical 
uv 


*MMA is the monomethylamine ion 


HIGH PERFORMANCE LIQUID 
CHROMOTOGRAPHY 

The first step in the scheme for the analysis of 
organic based explosives is to wash the debris with 
an organic solvent, such as acetone. After concen¬ 
tration and/or clean-up the sample is ready for 
analysis by HPLC. 

HPLC is an excellent method for the separation 
and identification of explosives and has the capa¬ 
bility for use in the area of quantitative analysis. 
The high sensitivity of HPLC lends itself well to 
explosive analysis in forensic matters, because as 
we have already noted, in bombing cases 
post-blast residues of big explosives usually are 
only found in trace quantities. 

Another asset that makes HPLC an excellent 
technique for explosive analysis is that some or- 

STANDARD ANIONS 


7 Eluent: 0.003M NaH C0 3 / 

O 0.0024M Na 2 C0 3 



Figure 6 . Separation of Common Anions. Peaks: Cl - , 
4ppm; NO" 2 , lOppm; HP0 4 -2 , 50 ppm; Br - , lOppm; NOj - , 
30ppm; S0 4 -2 , 504ppm. 


Li + 



Minutes 

Figure 7. Separation of Common Cations. Elvent: 0.01NHC1/ 
30% MeOH Column: Standard Dionex Separator Column. 
Peaks: Li + , lOppm; Na + , lOppm; NH + 4 , lOppm K + , lOppm. 

ganic explosives are thermally unstable making 
GC analysis difficult. HPLC, however, can be run 
at ambient temperatures nullifying this problem. 

Instrumentation 

The instrumentation of the IAU is a Waters Li¬ 
quid Chromatography System equipped with a 
Model 6000A chromatography pump and a 10 ul 
sample loop. The system utilizes a Waters Model 
440 dual wavelength absorbance detector operat¬ 
ing at 282 and 254 NM. 

In addition, the IAU has also adopted a Kratos 
variable wavelength ultraviolet detector at 210 
NM and a Thermal Energy Analyzer (TEA) detec¬ 
tor to the HPLC system. Figure 8 shows a block 
diagram of the HPLC set-up utilized by the IAU. 



Figure 8 . Block Diagram of HPLC Set-Up. 


75 







































In explosive analysis both reverse phase and 
normal phase HPLC systems are used. The gen¬ 
eral conditions of both systems are shown below: 
reverse phase conditions 

mobile phase: acetonitrile/ 
water (65/35) 

column: Waters u-Bondapak 
(3.9 mm x 30 cm) 
normal phase conditions 

mobile phase: methylene chloride/ 
ISO-octane (50/50) 
column: Waters uPorasil 
(3.9 mm x 30 cm) 

Applications 

There are four basic applications of HPLC to 
explosive analysis as applied by the IAU. They are 
as follows: 

(1) Trace analysis of explosives in both pre- 
and post-blast situations. 

(2) Identification and comparison of pre¬ 
blast explosives 

(3) Identification and comparison of smoke¬ 
less powders 

(4) Head space analysis 

There are two aspects of trace analysis; 
post-blast and pre-blast. Figure 9 shows the sepa¬ 
ration of four different common explosives which 
can be used as and explosive screen. An unknown 
explosive would be seen under the exact same con- 



Minutes 

Figure 9. HPLC of Explosive Screen. 


ditions and the retention times compared. 

Figure 10 shows a liquid chromatogram from an 
actual case. In this case the liner of a carrying case 
or bag was suspected of being used to carry explo¬ 
sives. Figure 10 shows the methylene chloride ex¬ 
tract of the bag liner. When using the uv detector 
at 254 nm. no traces of NG or EGDN, two explo¬ 
sives found in dynamite, could be found in the 
complex matrix which included several plasticiz¬ 
ers. 

Figure 11 shows the same methylene chloride 
extract analyzed using the TEA detector. Not only 
was EGDN and NG found but also traces of 
PETN. The TEA detector is a - NO? functional 
group specific detector and little of the complex 
matrix seen in Figure 10 was detected. 

HPLC is also used to identify and compare ma¬ 
terials that are known or believed to be explosives. 
Figure 12 shows the chromatogram of a dichloro- 
ethane extract of Unigel dynamite. This chroma¬ 
togram might be compared with the chroma¬ 
togram of another dynamite extract to determine 
if they are the same. These type of comparisons 
are important in association various explosives 
with terrorist groups which often use the same ex¬ 
plosive in several different bombings. HPLC is a 
very valuable tool to make these comparisons. 

HPLC is also used as the main method of analy¬ 
sis for head space examinations. Figure 13 is a 
chromatogram of a head space sample taken from 
the bombing debris of an actual case. It was deter¬ 
mined from the chromatogram that dynamite was 
the explosive used in the bombing. 



Figure 10. HPLC of Bag Liner Solvent Wash Using UV De¬ 
tector. 


76 

































0 10 20 
Minutes 


Figure 11. HPLC of Bag Liner Solvent Wash Using TEA De¬ 
tector. 

GAS CHROMATOGRAPHY/MASS 
SPECTROSCOPY 

The last instrumental method to be highlighted 
is GC/MS. As can be seen in Figure 1, GC/MS fits 
in the general scheme of explosive analysis one of 
two ways. It can either be the next step after the 
clean-up procedure or it can be the final step after 



Minutes 


Figure 12. HPLC of Hercules Unigel Dynamite Wash. 


the HPLC analysis. In this capacity it would serve 
directly as a confirmation technique. It is in this 
manner that GC/MS is primarily used by IAU. In 
either capacity GC/MS is a valuable tool in explo¬ 
sive analysis and can provide a great deal of struc¬ 
tural and compositional information about the 
sample. 

Instrumentation 

While the FBI Laboratory has available for its 
use several GC/MS systems in the IAU, the instru¬ 
ment primarily used is a Hewlett-Packard 5982A 
Dual Source GC/MS. The GC is a Hewlett-Pack¬ 
ard 5710A. Two different columns are used in the 
GC; one, a non polar column, 2mm x 74 cm, 
packed with 2°7o SP-2100 on 100/120 mesh Suple- 
coport; the other column, one of moderate polar¬ 
ity, is also a 2mm x 74 cm glass column packed 
with 3% SP 2250 on Supelcoport. 

In the MS system the ionization sources are as 
follows: for electron import (El) is 70 eV; while 
the chemical ionization source (GI) is methane. 
The mass analyzer is a quadrupole; while the de¬ 
tector is an electron multiplier. 

Applications 

There are four basic applications of GC/MS to 
explosives. Each will be briefly noted. 

The first application is the analysis of unknown 
compounds. GC/MS can supply compositional 
and structural information about the material. 
This application is most often used after the 
clean-up of the organic solvent most common and 



Minutes 


Figure 13. HPLC of Dynamite Head Space. 


77 


































100 - 


a - SULFUR in SMOKELESS POWDER 


160 



m i iii nnn~nT >|iiii Tm | t Th ti t »|tit t tii h iiii ii np i fr m i| nn n ii|i n i i H i| nn unp i n m i p i i n| i n i i i i i|in i iii i |ii n m i| 

180 200 220 240 260 280 300 320 


Figure 14. GC/MS of sulfur in Smokeless Powder. 


traditional use of GC/MS in explosive analysis. 

A second application is with head space and 
trace vapor analysis. Earlier in this paper the head 
space analysis procedure was outlined. Instead of 
the final analysis step being HPLC, it can be 
GC/MS. 

Another application of GC/MS is the analysis 
of solid and HPLC fractions by direct probe. In 
this application GC/MS is used as a conformitory 
technique of an HPLC analysis. Figure 14 shows 
the direct probe mass spectrum of an LC fraction 
of a smoleless powder specimen. The mass spec¬ 
trum is that of sulfur. 

A fourth application of GC/MS to explosives is 
the analysis of hydrocarbons. This analysis be¬ 
comes important when examining such explosives 
as ANFO, ammonium nitrate and fuel oil. Figure 
15 shows the total ion spectrum of a fuel oil found 
in a homemade ANFO explosive. The identifica¬ 
tion and characterization of the fuel oil becomes 
important if the same material consistently is used 
by terrorist group because it could become a trade¬ 
mark or means of establishing the identity of the 
group in unclaimed bombings. 

In conclusion, the IAU has been using the 
scheme which has been highlighted in this paper 
for almost two years with a great degree of suc¬ 


cess. In every instance the scheme may not be re¬ 
ligiously followed as it is only meant to be a gener¬ 
al guide. It is especially useful for someone who is 
just starting out in the field of explosive analysis. 
It should also be noted these are the methods of 
preference of the IAU and other techniques, such 
as IR, TLC, GC and DTA are all also useful and 
can be excellent techniques for explosive analysis. 



Figure 15. GC/MS of Fuel Oil found in ANFO Explosive. 


78 















NONIDEAL DETONATION BEHAVIOR OF SUSPENDED EXPLOSIVES 
AS OBSERVED FROM UNREACTED RESIDUES 


Yael Miron ', Richard W. Watson 1 2 , and J. Edmund Hay ! 
Pittsburgh Research Center 
Bureau of Mines 
U.S. Department of the Interior 


ABSTRACT. An investigation was conducted by the Bureau of Mines to recov¬ 
er, collect, and identify the solid explosion products of commercial explosives. 
These condensed products can include unreacted, partially reacted, and completely 
reacted ingredients. Various unconfined commercial explosives were fired sus¬ 
pended in a sphere in air. The solid residues were collected and studied. Unex¬ 
pectedly large amounts of residues were found. In general, the granular explosives 
produced more residue than the simigels and water gels. Many of the residues were 
found to be thermally reactive, not unlike the original explosives, when they were 
evaluated by thermal analysis test. The residues from the water gel explosives were 
the least reactive themally. Preferrential consumption of the ingredients was in¬ 
dicated by wet chemical analyses of a few of the residues. Residues were also col¬ 
lected from two semiconfined charges and one confined charge fired in cannon 
tests. As expected, the amounts of these residues were much smaller. A good in¬ 
verse correlation was found between the amount of unreacted residue and the 
square of the ratio of unconfined and confined detonation velocities, (D uncon- 
fined/D confined)2, in agreement with the hydrodynamic theory of detonation. 


INTRODUCTION 

Coal mine atmospheres contain coal dust and 
methane (natural gas), which can be ignited, or 
even exploded, under certain conditions. The ex¬ 
plosives used in coal mining are possible ignition 
sources, and therefore they are required to under¬ 
go and pass a battery of incendivity tests before 
they can be approved for use in underground coal 
mines. 

High pressures, shock waves, high-temperature 
gaseous products, and hot condensed particles all 
result from a detonation of an explosive charge. 
They can all singly or collectively ignite a dusty 
and gaseous atmosphere, if they possess the re¬ 
quired energy. Whereas the ability of shock waves 
and of hot gases to ignite flammable coal mine at¬ 
mospheres has been studied in some detail, the 
specific role of hot condensed particles in the igni¬ 
tion process of coal mine atmospheres has not 
been assessed to the same extent. Hot condensed 


1 Chemical Engineer 

2 Supervisory Research Physicist 
2 Supervisory Research Physicist 


particles can be viewed as hot surfaces supplying 
energy, or as catalytic surfaces enhancing the igni¬ 
tion process, for example, by releasing oxygen 
while decomposing. 

It was presumed that at least some of the hot 
particles would remain as a solid residue, and 
therefore it was decided to collect and observe the 
condensed residues from various explosives. 

EXPERIMENTAL WORK 
Instrumentation—Suspended Shots 

A large steel sphere, 3.7 m in diameter, with 
suitable hardware was modified and used for deto¬ 
nating the explosive charges and for containing 
the residues. The inside surface of the steel sphere 
was metallized with aluminum and in general 
withstood the effects of the explosions’ gaseous 
and condensed products. 

A vacuum pump with an in-line 5-micrometer 
sintered brass filter was used in a large number of 
the tests for removal of the gaseous explosion 
products. In later tests a circulating pump was 
used to remove the gaseous products and intro- 


79 



duce fresh air into the sphere. 

A vacuum cleaner, fitted with a new, preweight¬ 
ed, paper bag for each test, was used to collect the 
powdered residues. 

Materials 

A variety of commercial explosives, which in¬ 
cluded granular, gelatinous, and water gel formu¬ 
lations, was tested. 

The granular and gelatinous formulations con¬ 
tain explosive oils such as mixtures of nitrogly¬ 
cerin with ethylene glycol dinitrate; nitrocellulose 
is another ingredient. In addition, they contain 
oxidizers and fuels such as ammonium nitrate and 
wood meal and salts such as sodium chloride. The 
gelatinous formulations, on the average, contain 
more explosive oil and nitrocellulose than do the 
granular formulations. Also, in general, their oxy¬ 
gen balance is closer to stoichiometric, their den¬ 
sity is higher, and they are more energetic than the 
granular explosives. 

The commercial explosives tested in this pro¬ 
gram were chosen from explosives sent to the Bu¬ 
reau of Mines for a variety of permissibility tests. 
On the whole, the rates of detonation of gelatin¬ 
ous explosives tested by the Bureau of Mines range 
from 3200 to 5600 m/sec, whereas the rates of de¬ 
tonation of granular explosives range from 1700 
to 3500 m/sec. 

The water gel explosives do not contain explo¬ 
sive oils or nitrocellulose. They contain salts such 
as ammonium nitrate, sodium nitrate, and sodium 
chloride, and other ingredients. All of these ingre¬ 
dients are blended in water, and the mixture is 
gelled with gelling agents such as guar gum. On 
the average, their rates of detonation range from 
3400 to 3800 m/sec [3]. 

In most of the suspended tests the weight of the 
explosive charge, inclusive of the wrapper, was 
336 grams, but some smaller and a few larger 
charges were also evaluated. When more than one 
cartridge was used, the end, or ends, of each cart¬ 
ridge was cut off, as necessary, and the cut ends 
were firmly butted together and taped with a 
strong tape. A few charges that were more fluid in 
consistency were wrapped in an additional wrap of 
lay-flat, seamless, polyethylene tubing, or were 
carefully transferred from the original wrap into 
the polyethylene tubing. The diameter of all the 
charges was 3.2 cm (114 inches), and their length 
ranged from about 27.7 cm to 40.6 cm, dependent 
on the density and weight of the explosive charge. 
In the tests using only one cartridge (charge weight 


less than 200 grams), the charge length was about 
20 cm. 

Initiator 

A No. 8 detonator was used in all the tests; it 
was completely inserted in one end of the charge. 

RESULTS 

The average amounts of solid residue collected 
from each explosive fired in the sphere in the sus¬ 
pended mode are presented in Table 1, as recov¬ 
ered weight-percent of initial total weight. On the 
average, 55 to 60 pet of the granular-type explo¬ 
sives were recovered. In the case of the gelatinous 
charges similarly fired, about 30 to 40 pet re¬ 
mained as condensed residue. A larger spread in 
the amount of recovered residue was found for the 
water gels; it ranged between 13 and 46.5 wt-pet, 
and the average was about 32. 

To the eye, essentially all the residues appeared 
as fine, grey or beige-grey powders. Large prills, 
globs of gelatinous explosive oil, or crystals of 
such ingredients as ammonium nitrate, sodium ni¬ 
trate, or sodium chloride, all of which are easily 
discerned by the unaided eye in many of the origi¬ 
nal formulations, were not observed in the collect¬ 
ed residues. When the residues were sieved, the 
major portion of shredded wrapper was found in 
the coarser sieves, while the explosive residue pow¬ 
der was found in the finer fractions. Most of it 
passed through sieve No. 40 (opening = 0.425 
mm). The portion of powder retained on sieves 20, 
30, and 40 did contain white grains, as well as 
some powder. The residues also contained extra¬ 
neous material from the detonator and from the 
vacuum cleaner brushes. This foreign material was 
carefully removed with tweezers. 

Most of the tests were done when the humidity 
was low, in order to avoid dissolution of the resi¬ 
dues, due to adsorption of moisture by the highly 
hygroscopic materials, such as ammonium nitrate, 
found in many of the residues. The sphere was 
thoroughly washed and dried between most tests 
and after each test in which the residue could not 
be collected due to the humidity. 

Residues of the Explosives as Related to their 
Detonation Velocities 

The hydrodynamic theory of detonation, and 
more specifically the grain-burning mode of reac¬ 
tion, was used to explain the results. According to 
this model of explosive reaction, the portion of the 
explosive that undergoes complete detonation, 


80 


Table 1. AMOUNT OF RESIDUE COLLECTED IN 
SPHERE FROM SUSPENDED EXPLOSIVES 
FIRED IN AIR 


Explosive type 
and key number 

Residue, 

wt-pct 

(unreacted portion) 

Granular: 


1792 

59.3 


1794 

37.6 


1847 

66.9 


1914 

63.6 


2002 

62.4 


1 2015 

39.7 


Average 

54.9 

Gelatinous: 


1649 

37.3 


1906 

32.3 


1930 

35.8 


1971 

41.3 


Average 

36.7 

Water Gels: 


1732 

37.3 


1749 

30.5 


1787 

28.7 


1810 

39.5 


1857 

46.5 


1862 

29.5 


2 1952 

13.0 


1.2 2014 

20.5 


2019 

42.4 


Average 

32.1 


1 Taggant particles added to explosive for ease of identifica¬ 
tion; 0.05 wt-pct of total explosive weight. 

2 Key Nos. 1952 and 2014 are the same explosive; variation in 
results for the two key numbers may be due to differential 
aging brought about by unequal storage time (a lower key 
number signifies longer storage time), to differences in com¬ 
position from manufacturing process, or to the presence of 
taggant particles (explosive batches containing taggant were 
specifically prepared for tests by the Bureau of Mines, PRC, 
and may have been formulated on a small scale). 

designated m, is a function of detonation velocity 
as follows: 



In this relationship, D,*, is the maximum attaina¬ 
ble detonation velocity (theoretically attainable at 
infinite charge diameter), and D is the actual 
detonation velocity. In our experiments, we can 
equate the collected residue with the unreacted 
portion, or 1 - m. 

The detonation velocities of some of the explo¬ 
sives used in our residue collection tests were 


measured in two configurations. In one configura¬ 
tion the charge diameter was 3.2 cm (1 'A inches)— 
identical to the size of the charges used for residue 
collection—and it was not confined (except for the 
lightweight paper or plastic wrapper). This veloc¬ 
ity is designated as Di'/ 4 . In the other configura¬ 
tion, Schedule 80 steel pipe [7.6-mm (0.300-inch) 
wall thickness] was used to confine charges 7.6 cm 
(3 inches) in diameter. This resultant detonation 
velocity is designated D 3 . The results of these 
measurements are presented in table 2 and in Fig¬ 
ure 1 , in which (Du/a/D ?) 2 values are plotted as a 
function of the portion of explosive that reacted. 
Although the D 3 values are probably smaller than 
Deo values in most of the cases cited here, they are 
deemed close enough to their respective Doo values 
to be fair approximations. To better approximate 
the Doo values would have required much larger 
amounts of explosives and special facilities for 
testing such amounts. Theoretical values of Doo are 
based on various assumptions—including the 
choice of equation of state to be used in calculat¬ 
ing these values—and do not always agree with ex¬ 
perimental values. Therefore, they were not used 
here. 

Good agreement exists between the m values 
obtained from the residues, and from the (Di>/ 4 / 
D ?) 2 results, for the granular explosives. Relatively 
good agreement can be seen for the respective wa¬ 
ter gel values, whereas for the gelatinous explo¬ 
sives there is the least but still fair agreement. 

CHEMICAL ANALYSIS OF THE RESIDUES 

Chemical analysis of explosives is usually done 
by standard wet chemistry methods. The type of 
explosive and its ingredients determine the sol¬ 
vents used to extract and separate the various 
chemicals, the order of extraction, and the analyti¬ 
cal procedures. The relatively large amounts of 
residues collected implied the presence of unre¬ 
acted ingredients, as well as of partially reacted in¬ 
gredients, from the original formulations. Based 
on this assumption, standard procedures for 
analysis of unfired explosives were utilized for the 
chemical analysis of residues as well. However, 
methods other than those usually utilized in the 
routine analysis of explosives at the Bureau of 
Mines were employed, as needed, for compounds 
not commonly present in explosives. These meth¬ 
ods included atomic absorption and atomic emis¬ 
sion spectroscopy, X-ray diffraction and infrared 
spectroscopy, and scanning electron microscopy. 


81 













Table 2. DETONATION VELOCITIES FOR THE VARIOUS TEST EXPLOSIVES AND RESIDUES COLLECTED FROM 
THESE EXPLOSIVES WHEN FIRED SUSPENDED IN AIR 


Detonation velocity, 


Explosive type 
and key number 

m/sec 

DU/4 

(original wrapper) 

D3 

(steel tube) 

r D1 V* i2 

1 d 3 J 

Residue, 

wt-pct 

(unreacted portion) 

Portion 

reacted, 

m 

Granular: 

1792 

2,375 

3,835 

0.38 

59.3 

0.41 

1914 

2,070 

3,309 

.39 

63.6 

.37 

2002 

2.308 

4,286 

.29 

62.4 

.38 

Average 

— 

— 

.35 

61.8 

.39 

Gelatinous: 

1649 

5,000 

6,000 

.69 

37.3 

.63 

1930 

5,422 

6,002 

.82 

35.8 

.64 

1971 

5,005 

5,294 

.89 

41.3 

.59 

Average 

— 

— 

.80 

38.1 

.62 

Water gels: 

1749 

3,750 

4,500 

.69 

30.5 

.69 

1857 

3,000 

4,390 

.47 

47.1 

.53 

1862 

3,529 

4,577 

.59 

29.5 

.70 

2014 

3,565 

4,737 

.57 

20.5 

.79 

2019 

3,750 

4,821 

.61 

42.4 

.58 

Average 

— 

— 

.59 

34.0 

.66 


CHEMICAL ANALYSIS RESULTS 

The main goal of the chemical analysis was to 
identify and quantify unreacted explosive ingre¬ 
dients, partially reacted ingredients, and end prod¬ 
ucts of completely reacted ingredients, and in this 
way to determine if preferential reaction of the 
various ingredients occurred, and to what extent. 


C\J_ 

ro 

O 


O 


1.0 


0.8 


0.6 — 


0.4- 


KEY 

O Water gels 
□ Gelatinous 
A Granular 


D / 
/ 

□ / 


/ 


Y— 


/ 


/ 


/ 


/ 


/ 


/ 


/ 
/ A 


/ 




o / / O 
/ 


__L 

0.2 0.4 0.6 0.8 

m, PORTION REACTED 


1.0 


Figure 1. The Square of the Ratio of Detonation Velocities 
versus Portion of Explosive That Reacted. 


Information of this kind can contribute to a better 
understanding of the actual detonation behavior 
of heterogeneous explosive formulations; in addi¬ 
tion, some insight into the possible incendive be¬ 
havior of the different ingredients of such formu¬ 
lations, as they undergo changes during and fol¬ 
lowing the detonation, might be gleaned from 
such an account. 

The analyzed residues are identified by test 
number as presented in Table 1A in the Appendix. 
Results of the analyses are shown in Tables 3 and 4 
as the percent weight of the original ingredients 
based on the commercially reported compositions. 
The results of chemical analysis of residues from 
granular and gelatinous explosives are given in Ta¬ 
ble 3, while Table 4 presents analysis results of one 
residue from a water gel slurry explosive. 

As can be seen in Table 3, the explosive oil was 
not recovered in any of the residues analyzed. 
Also, on the average, ammonium nitrate was re¬ 
covered in smaller quantities, percentagewise, 
than was sodium nitrate, based on original 
amounts. Water and nitrocellulose were present in 
the original explosives in very small quantities, so 
that small errors in analysis can lead to large er¬ 
rors in the values of percent recovered. Hence, 
these values can be disregarded. Also, moisture is 
easily picked up by residue ingredients, such as 


82 














Table 3. PERCENT WEIGHT OF ORIGINAL > EXPLOSIVE INGREDIENTS RECOVERED IN RESIDUES FROM GRANU¬ 
LAR AND GELATINOUS EXPLOSIVES 


Key Number. 

Test 15 

Test 20 

Test 21 

Test 23 

Test 32 

1906 

1906 

1794 

1792 

1930 

h 2 o 

37 

24 

89 

93 

73 

Explosive Oil 

0 

0 

0 

0 

0 

NH 4 NO 3 

25 

17 

32 

47 

22 

NaN0 3 

61 

72 

~ 101 

~ 105 

60 

NH 4 CI 

2 

2 

2 

2 

101 

NaCl 

34 

37 

57 

87 

2 

CaC0 3 

38 

27 

15 

29 

168 

C.C.M.3 

56 

43 

43 

50 

83 

Nitrocellulose 

179 

72 

2 

2 

0 

Wrapper, paper 

4 

4 

39 

55 

4 

Wax 

4 

4 

39 

40 

4 


1 Based on chemical analysis by the Bureau of Mines, PRC 

2 Not present in original formulation. 

3 Combustible carbonaceous material. 

4 Not analyzed. 


ammonium nitrate, and will affect the results for 
water. 

The results in Table 4 for a residue collected 
from a water gel explosive (Test 27) are in many 
respects of a similar nature to the results shown in 
Table 3. That is, some ingredients, such as amine 
nitrates, were not recovered at all. Others were 
found in the original form as well as in decom¬ 
posed form. For instance, both calcium nitrate 
and its insoluble decomposition product, calcium 
oxide, were recovered. Nitrite ion was found in the 


Table 4. PERCENT WEIGHT OF ORIGINAL ' EXPLO¬ 
SIVE INGREDIENTS RECOVERED IN THE 
RESIDUE OF A W ATER GEL EXPLOSIVE 


Key No. 

Mode of Test. 

Test 27 

1810 

Suspended 

h 2 o 

32 

Amine nitrate sensitizer 

0 

nh 4 no 3 

0 

NaCl 

72 as NaCl 


22 as NaN0 3 

Ca(N0 3 h 

27 as Ca(N0 3 ) 2 


25 as Ca(N0 2 ) 2 


25 as CaO 

Aluminum 

96 

C.C.M. 

30 2 


■ Based on commercially reported compositions. 

2 Contains plastic wrapper and guar gum which were not 
analyzed separately. 


residue and was “assigned” as calcium nitrate, an 
intermediate decomposition product of calcium 
nitrate, although calcium nitrite itself was not 
identified as such. Sodium nitrate, not an original 
ingredient, was found in the residue as well. Infra¬ 
red and X-ray diffraction spectroscopy were used 
in an effort to verify the presence of the sodium 
nitrate and the various calcium compounds. 
Sodium nitrate peaks were prominent in the X-ray 
diffraction spectra, as were peaks of sodium 
chloride and aluminum, whereas calcium com¬ 
pounds were not observed. The infrared spectrum 
did not contain well defined peaks of any of the 
calcium compounds in the residue, but the overall 
spectrum resembled spectra of hydrated calcium 
nitrate compounds. Finally, scanning electron mi¬ 
croscopy (SEM) was utilized to observe the residue 
particles visually, and see if, possibly, the calcium 
compounds were amorphous and therefore were 
not seen in the X-ray spectra. Cubic crystals of 
sodium chloride were the only identifiable cry¬ 
stals. Their sizes were roughly between 1 and 10 
fim. Some clusters that appear to be particles stuck 
together by surface melting were also observable. 
Fusion, undergone by some portions of the 
residue, is evident in the SEM micrographs of 
higher magnifications. Particles of similar appear¬ 
ance were observed in residues from Tests 24 and 
28, utilizing the same explosive as in Test 27. The 
residue from Test 28 was partially analyzed. Com¬ 
positions of the residues from Tests 27 and 28 


83 













were similar, including the presence of sodium ni¬ 
trate in both. 

THERMAL ANALYSIS OF THE RESIDUES 

Thermal analysis is very helpful in the identifi¬ 
cation of single compounds, via their melting tem¬ 
perature, or the temperature of solid phase 
changes that they undergo. In the case of a mix¬ 
ture of two compounds that do not react chemical¬ 
ly or form a eutectic, thermal analysis is also of 
aid. When more than two compounds are present 
in a mixture, thermal analysis is utilized mainly 
for assessing the overall thermal behavior of the 
mixture. 

The instruments used in thermal analysis are 
sensitive and respond best to small samples, of the 
order of a few milligrams. The explosives are 
heterogeneous mixtures containing both liquids 
and solids, the latter of varying sizes. The residues 
are also multicomponent solid mixtures. Larger 
samples are required for good representation, and 
samples of about 50 mg were utilized. 

A Du Pont 990 differential scanning calorimeter 
(DSC) (reference to specific makes and models of 
equipment and suppliers is made for identification 
purposes only and does not imply endorsement by 
the Bureau of Mines) was employed in the thermal 
tests, which were done in an atmosphere of static 
air, at a heating rate of 10° C/min. Fine glass 
beads were used as reference material. A quantita¬ 
tive thermal analysis was not sought here, only an 
overview of thermal behavior of the original ex¬ 
plosives versus their resultant residues. 

THERMAL ANALYSIS RESULTS 

A gelatinous-type explosive (Key No. 1906) 
used in Tests 15 and 20 was evaluated in the DSC. 
A thermogram of a small sample of this explosive 
appears in Figure 2, thermogram A. A small 
sample of the residue of Test 15 gave the thermo¬ 
gram B which is seen in Figure 2, whereas thermo¬ 
gram C in Figure 2 is for a larger sample of the 
same residue. A large sample of residue was uti¬ 
lized to obtain the thermogram for the residue 
from Test 20, which is seen in Figure 2, thermo¬ 
gram D. 

Another gelatinous explosive (Key No. 1930) 
was used in Test 32; its thermogram is shown in 
Figure 3, thermogram A, while the residue from 
this test gave thermograms B and C in Figure 3 for 
a large and small sample, respectively. 

Two granular explosives, Key Nos. 1794 and 
1792, were evaluated in Tests 21 and 23, respec¬ 


tively. Thermograms of the original explosives 
were not obtained because the explosives were not 
available any more. Thermograms of the residues 
are shown in Figure 4; thermogram A was found 
for Key No. 1794 and thermogram B is for Key 
No. 1792. 

In addition to gelatinous and granular explo¬ 
sives, water gel explosives were also tested. One 
water gel explosive, Key No. 1810, was fired in 
Tests 27 and 28. Figure 5, thermogram A was ob¬ 
tained for the original explosive, while thermo¬ 
grams from the residues of Tests 27 and 28 are de¬ 
picted in thermograms B and C of Figure 5, re¬ 
spectively (Disregard thermogram D as it does not 
pertain to this discussion.) Finally, another water 
gel explosive, Key No. 1942, fired in Test 36 has 
the thermograms shown in Figure 6, thermogram 
A and B, for the original formulation and for the 
residue, respectively. 

DISCUSSION OF RESULTS 

Preferential consumption of the explosive ingre¬ 
dients was indicated in the residues that were ana¬ 
lyzed. For example, explosive oil (usually nitrogly¬ 
cerin with ethylene glycol dinitrate) was consumed 
completely, while other ingredients such as ammo¬ 
nium nitrate, sodium nitrate, and sodium chloride 
were only partially consumed or decomposed to 
various degrees. The large amounts of residues re¬ 
covered were unexpected. Also unexpected was 
the fact that ingredients such as ammonium ni¬ 
trate which decompose at low temperature re¬ 
mained partially unreacted. Sodium nitrate, which 
decomposes at a higher temperature, for the most 
part did not take part in the detonation and was 
recovered almost intact (60 to 100 wt pet of the 
original sodium nitrate was found in the analyzed 
residues from the suspended shots). 

Although the possibility of incomplete reaction 
is cited by the many research workers in the explo¬ 
sives field, not much detailed information is avail¬ 
able on the subject. Therefore comparisons are 
difficult. Beyling and Drekopf (/) observed appre¬ 
ciable amounts of unexploded ingredients in the 
products of commercial blasting agents tested in 
actual field conditions. The composition of the 
unexploded portion was reported by them to be 
similar to the composition of the original formula¬ 
tion. 

Craig et al. (2) measured detonation rates of a 
confined water gel explosive, using 10.16- and 
20.23-cm-diam clay pipes. The experimental 
detonation rates were much lower than the theo- 


84 


retically calculated values. Residues were not col¬ 
lected by Craig et al.\ however, they propose in¬ 
complete reaction as the explanation for the dif¬ 
ferences between the measured and calculated 
detonation velocities. Furthermore, their calcu¬ 
lated, theoretical detonation rates do agree with 
experimental values when it is assumed that am¬ 
monium nitrate failed to react in the sample of 
larger diameter. Similarly, for a good agreement 
between theoretical and experimental detonation 
rates for the small size charge, one has to assume 
that other ingredients, in addition to ammonium 
nitrate, do not react completely. 

The concept of “ion exchange” has been 
evoked to explain the less incendive behavior of 
explosive formulations containing sodium nitrate 
and ammonium chloride in flammable coal mine 
atmospheres. 

The two ion pairs, 

NaNOj -F NHjCl ^ NH4NO3 + NaCl, [ 1 ] 
are theoretically equivalent as far as the total 
available energy that can be released by each pair 
in a detonative reaction is concerned. But if each 
salt reacts at a different rate, so that its contribu¬ 
tion to the total energy released in the detonative 
reaction zone (ahead of the C-J layer) is different, 
then these pairs are not equivalent, especially 
when the explosive charge is not confined and por¬ 
tions of the ingredients do not react at all. 

The presence of sodium nitrate in two residues 
from one water gel explosive (Key No. 1810) not 
containing sodium nitrate as an original compo¬ 
nent raises some questions about the actual com¬ 
positions of water gels at the time that they are 
fired. Although it is not conclusively known if the 
sodium nitrate was formed in the detonation, or 
was present in the original explosive charge, the 
latter is thought to be the case. Ammonium nitrate 
and sodium chloride can undergo metathesis, or 
double decomposition, as follows: 

NFL4NO3 + NaCl^NFFCl + NaNO, [2] 

This reaction could occur in storage during tem¬ 
perature changes which affect the solubilities of 
the various salts. And indeed results from other, 
unrelated tests suggest that sodium nitrate is 
present in the original explosive prior to detona¬ 
tion. In the winter months, when temperatures are 
low, the solubility of sodium nitrate decreases and 
it can precipitate out inside the water gel. 

Anhydrous calcium nitrate melts at ~ 561° C 
and at temperatures higher than the melting point 
decomposes to the nitrite by evolving oxygen. On 
further heating to higher temperature, calcium 


oxide forms, concurrent with evolution of nitro¬ 
gen oxides. Consideration of the results in Table 4 
leads to the conclusion that a portion of calcium 
nitrate undergoes complete reaction to calcium 
oxide when it is a constituent of a water gel explo¬ 
sive that is fired in a suspended, unconfined mode. 
We can reasonably surmise that increased confine¬ 
ment will increase the amount of calcium nitrate 



0 100 200 300 400 

SAMPLE TEMPERATURE, °C 


Figure 2. Thermograms of a Gelatinous Explosive (Key No. 
1906) and of its Residue. 

A. Original composition. 

B. Residue: Test 15 (fine powder from sintered filter in 
vacuum pump line). 

C. Residue; Test 15. 

D. Residue; Test 20. 


85 










































































































ENDOTHERMIC ! EXOTHERMIC 


that is converted to the oxide. 

Fine aluminum powder, when a component of 
an explosive formulation, is considered as a con¬ 
tributor to the incendive behavior of the explosive. 
It can burn in air to form aluminum oxide and re¬ 
lease large amounts of energy in the process. But 
most of the aluminum from the explosive fired in 
Test 27, unconfined, was recovered in the residue 
unchanged. 

We have checked for the presence of nitrite in 
the analyzed residues that contained sodium 
nitrate as an original ingredient, but did not detect 
any in spot tests. A more careful analysis is 
needed, because many of the ingredients found in 
the residues interfere in the tests for nitrite. 

Although the residues differ in composition 
from the original formulations, many of them 



Figure 3. Thermograms of a Gelatinous Explosive (Key No. 
1930) and of its Residue. 

A. Original composition. 

B. Residue; Test 32, Large sample. 

C. Residue; Test 32, Small sample. 


possess a combination of ingredients that is exo¬ 
thermic, as shown by the thermograms in Figures 
2 and 3 for two gelatinous explosives. Without 
going into great detail about the various aspects of 
the thermograms, we can say that the residues are 
quite similar in thermal behavior to the parent 
compositions; the only difference of importance is 
the temperature at which exothermic behavior is 
initiated. The temperature of initiation of exo¬ 
thermic behavior is lower for the original explo¬ 
sives than for their respective residues. Thermo¬ 
grams of residues from two granular explosives, 
comparable in composition, are presented in 
Figure 4. The parent explosives were not available 
any more when the thermograms were obtained, 



Figure 4. Thermograms of the Residues of Two Granular Ex¬ 
plosives. (a) Key No. 1794; (b) Key No. 1792. 

A. Residue; Test 21, Key No. 1794. 

B. Residue; Test 23, Key No. 1792. 


86 






























































































































































































































































but the thermograms of the residues are similar in 
most aspects to thermograms of the same explo¬ 
sives, but of different key numbers. This was ex¬ 
pected, since one residue contains about 60 per¬ 
cent of the original charge; the other residue con¬ 
tains about 40 percent of the original charge. The 
high degree of exothermicity is clearly evident in 
the thermograms. The water gels on the whole 
have undergone more reaction in our tests, and 
their residues contain less reactive material. This is 
evident when the thermograms of the parent ex¬ 
plosive and its residue are compared, as in Figures 
5 and 6, which are self-explanatory. The thermal 
analysis results indicate that large amounts of resi¬ 
due, which can accumulate in sites where uncon¬ 
fined granular or gelatinous explosives are fired, 
can constitute a hazard. On the other hand, in 
cases of sabotage, if explosives are used in an un¬ 
confined mode, they may be more easily detect¬ 
able. One of the difficulties in identification is 
their appearance. They look more like soil or dust 
than like explosives. 

SUMMARY 

Chemical analysis of a few of the residues shows 
that their composition is not identical to the orig- 



Figure 5. Thermograms of a Water Gel Explosive (Key No. 
1810) and of its Residue. 

A. Original composition. 

B. Residue; Test 27. 

C. Residue; Test 28. 

D. Residue; Test 40. 



0 100 200 300 400 


SAMPLE TEMPERATURE, °C 

Figure 6. Thermograms of a Water Gel Explosive (Key No. 
1952) and of its Residue. 

A. Original composition. 

B. Residue; Test 36. 

inal composition. Rather, preferential reaction 
has been observed. Ingredients such as explosive 
oil were not recovered at all, while various per¬ 
centages of most of the other ingredients were re¬ 
covered. Sodium nitrate was among the least con¬ 
sumed. The presence of nitrite in one residue was 
gratifying, because it was specifically looked for. 
The presence of compounds that are formed by 
different stages of decomposition suggests that 
consecutive reactions can take place in the explo¬ 
sion process, or its aftermath, and that reaction 
gases, such as oxygen and nitrogen oxides, evolved 
during these reactions, may act as sensitizers and 
enhance the probability of ignition of natural gas, 
coal dust, or both. 

For purposes of recovering residues in cases of 
sabotage, it would be advantageous to remember 
that the residues look like soil or dust, and thus 
are not easy to identify visually. Also, it should be 
kept in mind that most of the commercial explo¬ 
sives contain ammonium nitrate and/or amine 
nitrates, all of which are highly hygroscopic. 
When exposed to the atmosphere, they will adsorb 
moisture and dissolve. The resultant solutions are 
usually acidic and in turn can dissolve foreign 
matter. 

The possibility of ion exchange either in storage 
or in the detonation can interfere in the identifica¬ 
tion of the original explosive from the analysis of 
its residue. For this reason some form of tagging 
for identification is still very appealing. 


87 






































































































































APPENDIX 


Table 1 A. SUSPENDED EXPLOSIVES FIRED IN SPHERICAL CHAMBER IN AIR WITH A NO. 8 DETONATOR ' 


Test 

No. 

Key No. 

Explosives tested 

Type 

Charge weight, 1 2 3 4 

g 

Residue 

wt-pct 

15 

1906 

Gelatinous 

185 

33 

20 

" 

" 

341 

26 

21 

1794 

Granular 

258 

38 

22 

1857 

Water Gel 

313 

47 

23 

1792 

Granular 

289 

55 

24 

1810 

Water Gel 

336 

43 

25 

" 

n 

336 

36 

26 

n 

n 

335 

40 

27 

" 

if 

336 

38 

28 

n 

n 

175 

40 

29 

n 

n 

169 

41 

30 

1906 

Gelatinous 

342 

38 

32 

1930 

n 

339 

34 

34 

1862 

Water Gel 

312 

30 

36 

1952 

ll 

336 

10 

44 

n 

n 

336 

16 

46 

1787 

n 

275 

29 

48 

// 

" 

336 

28 

50 

1732 

n 

336 

37 

52 

1749 

n 

336 

27 

60 

1649 

Gelatinous 

336 

35 

62 

3 2015 

Granular 

336 

40 

64 

1971 

Gelatinous 

336 

41 

66 

n 

n 

336 

39 

72 

n 

n 

336 

43 

74 

" 

n 

509 

42 

76 

n 

n 

4 336 

51 

78 

1792 

Granular 

336 

64 

80 

2019 

Water Gel 

336 

42 

82 

1749 

n 

336 

35 

84 

3 2014 

il 

336 

21 

86 

2002 

Granular 

336 

63 

88 

1649 

Gelatinous 

336 

40 

90 

2002 

Granular 

336 

62 

92 

1914 

II 

336 

64 

94 

2014 

Water Gel 

336 

20 

96 

1930 

Gelatinous 

336 

37 

98 

1848 

Granular 

192 

67 


1 Key No. C-1832 

2 Charge weight includes the weight of wrapper used in each test. 

3 Taggant added to explosive for identification purposes. 

4 2.5 g tetryl booster was used. 


ACKNOWLEDGEMENTS 

The authors acknowledge Mr. Thomas C. Ruhe 
for the careful preparation of the sphere facility, 
and for his valued participation in the experi¬ 
ments. Thanks are due Mr. Charles F. Swab, Jr. 
for some of the chemical analyses. 


REFERENCES 

1. Beyling, C., and K. Drekopf. Sprengstoffe and 
Zundmittel (Explosives and Ignition Materials), 
Julius Springer Verlag, Berlin, Germany, 1937, 
as quoted in Melvin A. Cook, The Science of 
High Explosives. Reinhold Publishing Corp., 
New York, 1958, pp 286-284. 


88 






2. Craig, B. G., J. N. Johnson, C. L. Mader, 
and G. F. Lederman. Characterization of Two 
Commercial Explosives. Report No. LA-7140 
(The University of California Report UC-45), 
May 1978. 


3. Ribovich, J., R. W. Watson, and J. J. Seman. 
Active List of Permissible Explosives and Blast¬ 
ing Devices Approved Before December 31, 
1975. MESA Informational Report 1046, 1976. 


89 













































































































































































































































INSTRUMENTAL METHODS 







































INSTRUMENTAL TECHNIQUES UTILIZED IN THE IDENTIFICATION OF 
SMOKELESS POWDERS. PROTON MAGNETIC RESONANCE (PMR) AND 

GAS CHROMATOGRAPHY (GC). 


RichardE. Meyers, M.S., and John A. Meyers, B.S., 
Forensic Science Branch, National Laboratory Center, 
Bureau of Alcohol, Tobacco and Firearms, 
and the 

Drug Enforcement Administration North Central Field Laboratory, 

respectively. 


ABSTRACT. An approach to identifying the manufacturer of domestic com¬ 
mercial smokeless powders has been evaluated at the Bureau of Alcohol, Tobacco 
and Firearms (ATF) National Laboratory Center and the Drug Enforcement Ad¬ 
ministration (DEA) North Central Field Laboratory. The procedure uses a combi¬ 
nation of proton magnetic resonance (PMR), and Gas Chromatography (GC). The 
use of PMR permits discrimination between similar products of the major U.S. 
manufacturers, namely, Dupont, Hercules, or Winchester-Western. Using PMR 
alone, some discrimination can be made within a particular manufacturer’s prod¬ 
ucts. The GC profile permits the observation of major and minor components. 
When PMR and GC data are combined types within a single manufacturer can be 
distinguished. These results were obtained using undetonated samples. This pre¬ 
sentation discusses the differences observed in both the PMR spectra and GC chro¬ 
matograms, including variations seen in products from different manufacturers 
and those in products from a particular manufacturer. Examples of the results 
showing both similarities and differences will be given. Potential application of the 
technique to typical forensic problems is described. 


An approach to identifying the manufacturer of 
domestic commercial smokeless powders has been 
evaluated at the Bureau of Alcohol, Tobacco and 
Firearms (ATF) National Laboratory Center and 
the Drug Enforcement Administration (DEA) 
North Central Field Laboratory. The procedure 
utilizes a combination of proton magnetic reso¬ 
nance (PMR), and gas chromatography (GC). 

A Forensic Chemist is often asked a question 
similar to the following: “Is the smokeless pow¬ 
der in the recovered and/or seized pipe bomb the 
same as that seized from the suspect?’’ It is appar¬ 
ent that for a definitive answer to this question, 
there is a need for a comparison method, which is 
effective both in distinguishing between similar 
products from different producers and different 
types produced by a single manufacturer. 

References 1 through 8 describe approaches to 
the examination of smokeless powder; however a 
definitive identification is not usually addressed. 
The main thrust of many of the articles is to iden¬ 
tify the smokeless powder as having come from a 


particular cartridge for gunshot residue examina¬ 
tion and not for explosive examinations. Each 
paper deals with only one aspect of the examina¬ 
tion and therefore does not give a definitive prod¬ 
uct identification. The literature does not deal 
with the question regarding the identification of 
the manufacturers of single and double base 
smokeless powders. 

This research was begun to determine the feas¬ 
ibility of utilizing proton magnetic resonance 
(PMR) and/or gas chromatography (GC) to iden¬ 
tify the various smokeless powders available com¬ 
mercially in the United States. It was soon found 
that each technique gave certain discrete informa¬ 
tion. The two techniques, in conjunction with a 
microscopic examination to determine the mor¬ 
phology (Table 1) of the sample allows identifica¬ 
tion of, not only the manufacturer, but also the 
various powders produced by the manufacturer, 
which is illustrated in Figure 1. Thin-layer 
chromatography was used to determine whether 
the smokeless powder was single-base (SB) or 


93 


Table 1. MORPHOLOGY OF SMOKELESS POWDERS. 


Improved Military Rifle (IMR) 

DUPONT 

I MR-3031 IMR-4198 IMR-4320 

I MR-4831 I MR-4064 IMR-4227 

IMR-4350 I MR-4895 

HERCULES 

Reloader 7 

HODGDON 

H-322 H-4227 H-4895 

H-4198 H-4831 


Ball and Flattened Ball 

WINCHESTER-WESTERN 
WW-230 WW-540 WW-571 WW-680 

WW-748 WW-760 WW-785 

HODGDON 

H-414 BL-C H-335 

Ball 

HODGDON 

H-380 H-870 


SR-4756 

Non-Perforaled Wafer 

DUPONT 

SR-7625 

800-X 

Bullseye 

HERCULES 

2400 Red-Dot 

Herco 

Green-Dot 

Unique 

Blue-Dot 

700-X 

Perforated W afer 

DUPONT 

PB 

WW-231 

Flattened Ball 

WINCHESTER-WESTERN 

WW-296 WW-452AA 

AL-5 

WW-473AA WW-630 

Flake (Diamond Shaped) 

S&W ALCAN 

AL-7 

AL-8 


double-base (DB) (Table 2)(9). A discussion of 
smokeless powder manufacture appears in the En¬ 
cyclopedia of Explosives and Related Items, pub¬ 
lished by Picatinny Arsenal (10, 11, 12). 

Gas chromatography (GC) has been used for 
the determination of plasticizers and stabilizers in 
composite double-base propellants and nitrated 
derivatives of glycerine (13, 14). A gas-liquid 
chromatographic method has also been developed 
for determining nitrate esters as well as stabilizers 
and plasticizers in a wide variety of nitrocellulose- 
base propellants (15). Proton magnetic resonance 
has been used by Picatinny Arsenal (16, 17, 18) for 
the identification of various explosive com¬ 
pounds. 


microscopic 



NUCLEAR MAGNETIC -GAS CHROMATOGRAPHY 

RESONANCE 


IDENTIFICATION TRIANGLE 

Figure 1. Identification Triangle. 


94 



Table 2. SINGLE-BASE AND DOUBLE-BASE PROPELLANTS. 



Single-Base 



Double-Base 



DUPONT 



DUPONT 


IMR-3031 

1 MR-4064 

IMR-4198 


700-X 800 

-X 

I MR-4227 

IMR-4320 

I MR-4350 




1MR-4831 

1 MR-495 

SR-4756 




SR-7625 

PB 









WINCHESTER-WESTERN 


S&W ALCAN 


WW-230 

WW-231 WW-296 

WW-452AA 




WW-473AA 

WW-540 WW-571 

WW-630 

AL-5 

AL-7 

AL-8 

WW-680 

WW-748 WW-760 

W'W-785 


HODGDON 



HERCULES 


H-322 

H-4198 

H-4227 

Reloader 7 

Bullseye 

Green-Dot 

H-4831 

H-4895 


2400 

Unique 

Red-Dot 




Blue-Dol 

HODGDON 

Herco 




BL-C 

H-335 

H-380 


H-414 H-870 


EXPERIMENTAL 

Apparatus. A commercial gas chromatograph, 
Hewlett-Packard 5880A with flame ionization de¬ 
tector (FID) was used in this investigation (Table 
3). Column packings were obtained from Applied 
Science Laboratories. A Varian model Em 390 nu¬ 
clear magnetic resonance (NMR) spectrometer 
was used to obtain the NM R-spectrum (Table 4). 


material. Approximately 500 mg of each smoke¬ 
less powder was placed in 1.0 ml of CDCf. The 
sample was allowed to stand in solution for at 
least 2 hours, and then half of the solvent was 
withdrawn and placed in an NMR tube. 

Approximately 100 mg of each smokeless 
powder was dissolved in 2.0 ml of Methanol 
(MEOH) for examination by GC. A 3.0 /ul sample 
was used for this purpose. 


Table 3. GAS CHROMATOGRAPHY CONDITIONS. 

Columns: 

6 ft x Vi. inch glass, 4 mm i.d. 
packed with 3% OV-17 on 100-120 mesh 
Gas Chrom Q 
Column temp 160-250°C 
Column temp program rate, 10°C/min. 

Detector temp 300°C 
Injection port temp 275 °C 
Nitrogen flow, 60 cc/min. 

Sample size, 3 A 


MAGNETIC RESONANCE CONDI- 


Table 4. NUCLEAR 
TIONS. 

Magnetic field strength 
Field frequency 
RF Power 

Filter Time Constant 
Reference 


21,140 gauss 
90 Mhz 
0.03 m G 
0.5 sec. 

Tetramethylsilane (TMS) 


Procedure. Deuterochloroform (CDC1 3 ) was se¬ 
lected as the NMR Solvent because of extraction 
problems with acetone. The smokeless powders, 
when dissolved in acetone, gelatinized and pre¬ 
vented the separation of the acetone from the solid 


RESULTS AND DISCUSSION 

Smokeless powders can be initially categorized 
by their morphology. Visually, perforated wafers 
or discs, non-perforated wafers, ball, flattened 
ball, cylinder, or flake propellants can be readily 
distinguished. Next, determine whether they are 
single-base (SB) or double-base (DB). These two 
initial steps considerably narrow the areas of con¬ 
sideration for type/brand identification. 

A PMR spectra is obtained to identify the 
manufacturer, and permit discrimination between 
similar products of the major U.S. manufacturers, 
namely, Dupont, Hercules, or Winchester-West¬ 
ern. At this point there is no absolute identifica¬ 
tion of the product type or brand name within the 
manufacturer’s line. Additional information is re¬ 
quired to distinguish company X’s product A 
from product B. The GC profile of the methanol 
extract of the sample permits the observation of 
major and minor components. Combining the 
PMR and GC data allows discrimination of types 
within the product line of a single manufacturer. 


95 


When, from other information, the sample is 
suspected of being a Hodgdon powder, it must be 
examined very carefully. Hodgdon is not a manu¬ 
facturer of smokeless powders. They purchase pri¬ 
marily from three basic sources: (1) ICI of Scot¬ 
land, (2) Winchester-Western, and (3) U.S. Gov¬ 
ernment surplus. From the spectra and chromato¬ 
grams obtained in this work, Hodgdon powders 
were differentiated from each other as well as 
other manufacturers. Presently, it is not known 
what causes these differences, however, they may 
arise primarily from blending. Since the U.S. Gov¬ 
ernment buys their powders from various manu¬ 
facturers and if no further processing is per¬ 
formed, the particular composition may change 
with time. Therefore, future Hodgdon powders 
may not be readily differentiated from other com¬ 
mercial smokeless powders. Examples of typical 
PMR spectra and GC chromatograms are given in 
Figures 2 through 19. 

As a result of this research project, it was deter¬ 
mined that there were several areas that needed to 


be considered for further work. The following is a 
listing of those areas of consideration. They have 
been placed in an order with the first being con¬ 
sidered the most important. This order of impor¬ 
tance may change. 

1. Additional Domestic Propellants. 

2. Propellants from other countries. 

3. Sensitivity. What is the smallest sample size 
that can be analyzed? 

4. Identification of the compounds in both the 
PMR Spectrum and GC Chromatograph. 

5. Can differences be seen when smokeless 
propellants have been added to each other? 

A. Same Brand 

B. Different Brands 

6. Differences within the same can of Propellant 
Powders. 

7. Differences within the same batch. 

8. Batch to Batch differences. 

9. Relative aging of Propellants. Are there any 
differences over a given time period? 

10. Detonated Smokeless Powders. 


96 



7 6 5 4 

Figure 2. PMR Spectra of Dupont IMR-4831. 


•dOMt 

410 

UO 




worn 

4(0 

1(0 


7!0 


3 '5 


1!0 


o 

-~ 4 ~- 4 -~ 


300 

120 


450 




7 6 5 4 3 

Figure 3. PMR Spectra of Flodgdon 4831. 


97 





































































































































































































I ' I I I II I I I I II I M I I I I r I I I I I 1 | I I ! I I 1 I I | I 1 1 1 1 ! ' 1 : 1 • 1 1 1 ■ i ■ : ' 1 I : ’ 1 : 



6 5 4 3 

Figure 4. PMR Spectra of Winchester-Western 680. 


doi 


'" T 1 ’ ' 1-TT^ 


t - r i ■ ft "]■ i' i n 1 1 ■ r h ” i i i i i | i i i i ] i i i i i t i i i i i 


r t r | 1 ~ T i I I I' TT I |T I M 



f 


4io 

1(0 


Hi I 

!.i- 


7i0 


3 '5 


h-b. 


150 


-I- H 


060 


300 


120 


i—r 


--F 


.-. 5 


30 I 


! 

F 4 ~+ 

4—t—I- 


-|— 


4~ 


,-U.l 


mv alcM al-t 




-i- 


10 



7 6 5 

Figure 5. PMR Spectra of S & W Alcan AL-7. 


98 







































































































































































Figure 6. Gas Chromatogram of Dupont IMR-4831. 



\ 

f 

HODG H 4831 


Figure 7. Gas Chromaiogram of Hodgdon FI-4831. 


99 























Figure 8. Gas Chromatogram of Winchester-Western 680. 



Figure 9. Gas Chromatogram of S & W Alcan AL-7. 


100 


































Figure 10. PMR Spectra of Hercules Red-dot. 



Figure 11. Gas Chromatogram of Hercules Red-dot. 


101 




























































































T~ —--f 


10 9 8 7 6 5 4 3 2 1 0 

Figure 12. PMR Spectra of Flercules Green-dot. 



Figure 13. Gas Chromatogram of Hercules Green-dot. 


102 



































































































































































































































• S/r 9WCCT 


EMOOF 3 



Figure 14. PMR Spectra of Hercules Blue-dot. 


i 

i 



103 











































































































t. 


Figure 16. PMR Spectra of Winchester-Western 230. 



\ 

\ 


\ . - 

> = ; • - 1 



1 

/ WW 230 


Figure 17. Gas Chromatogram of Winchester-Western 230. 


104 





































































































































































































Figure 18. PMR Spectra of Winchester-Western 231. 



i 

t_ 

r 


WW 231 


Figure 19. Gas Chromatogram of Winchester-Western 231. 


105 


CO 





























































































REFERENCES 

1. DeHaan, J. D., “Quantitative Differential 
Thermal Analysis of Nitrocellulose Propel¬ 
lants,” Journal of Forensic Sciences, Vol. 20, 
No. 2, April 1975, pp. 243-253. 

2. House, Jr., J. E. and Zack, P. J., “Thermal 
Decomposition of Nitrocellulose Propellants,” 
Journal of Forensic Sciences, Vol., 22, No. 2, 
April 1977, pp. 332-336. 

3. Zack, P. J., and House, Jr., J. E., “Propel¬ 
lant Identification by Particle Size Measure¬ 
ment,” Journal of Forensic Sciences, Vol. 23, 
No. 1, Jan. 1978, pp. 74-77. 

4. Mach, M. H., Pallos, Andrew; and Jones, 
P. F., “Feasibility of Gunshot Residue Detec¬ 
tion Via Its Organic Constituents. Part 
I: Analysis of Smokeless Powders by Com¬ 
bined Gas Chromatography - Chemical Ioniza¬ 
tion Mass Spectrometry,” Journal of Forensic 
Sciences, Vol. 23, No. 3, July 1978, pp. 
433-445. 

5. Mach, M. H.; Pallos, Andrew; and Jones, 
P. F., “Feasibility of Gunshot Residue Detec¬ 
tion Via Its Organic Constituents. Part II: A 
Gas Chromatography - Mass Spectrometry 
Method,” Journal of Forensic Sciences, Vol. 
23, No. 3, July 1978, pp. 446-455. 

6. Newlon, N.A., and Booker, J. L., “The Iden¬ 
tification of Smokeless Powders and Their Resi¬ 
dues by Pyrolysis Gas Chromatography,” Jour¬ 
nal of Forensic Sciences, Vol. 24, No. 1, Jan. 
1979, pp. 87-91. 

7. Hardy, D. R., and Cher a, J. J., “Differentia¬ 
tion Between Single-Base and Double-Base 
Gunpowders,” Journal of Forensic Sciences, 
Vol. 24, No. 3, July 1979, pp. 618-622. 

8. Peak, S. A., “A Thin-Layer Chromatographic 
Procedure for Confirming the Presence and 
Identity of Smokeless Powder Flakes,” Journal 
of Forensic Sciences, Vol. 25, No. 3, July 1980, 
pp. 679-681. 

9. Midkiff, Jr., C. R., and Washington, W. D., 
“Systematic Approach to the Detection of Ex¬ 
plosive Residues. Part III. Commercial Dyna¬ 
mite,” Journal of Assoc, of Off. Anal. Chem¬ 
ists, Vol. 57, No. 5, 1974, pp. 1092-1097. 

10. Fedoroff, B. T., and Sheffield, O. E., “En¬ 


cyclopedia of Explosives and Related Items,” 
PATR 2700, Picatinny Arsenal, Dover, New 
Jersey. Vol. 2, pp. B-l 1 - B-16. 

11. Fedoroff, B. T., and Sheffield, O. E., “En¬ 
cyclopedia of Explosives and Related Items,” 
PATR 2700, Picatinny Arsenal, Dover, New 
Jersey. Vol. 7, pp. FI-65 - H-72. 

12. Fedoroff, B. T., and Sheffield, O. E., “En¬ 
cyclopedia of Explosives and Related Items,” 
PATR 2700, Picatinny Arsenal, Dover, New 
Jersey. Vol. 7, p I 64. 

13. Trowell, J. M., and Philpot, M. C., “Gas 
Chromatographic Determination of Plasticizers 
and Stabilizers in Composite Modified Dou¬ 
ble-Base Propellants,” Analytical Chemistry, 
Vol. 41, No. 1, Jan. 1969, pp. 166-168. 

14. Trowell, J. M., “Gas Chromatographic De¬ 
termination of Nitrated Derivatives of Glyce¬ 
rine in Aged Double-Base Propellants,” Analy¬ 
tical Chemistry, Vol. 42, No. 12, Oct. 1970, pp. 
1440-1442. 

15. Alley, B. J. and Dykes, H. W. H., 
“Gas-Liquid Chromatographic Determination 
of Nitrate Esters, Stabilizers, and Plasticizers in 
Nitrocellulose-Base Propellants,” Journal of 
Chromatography, Vol. 71, No. 1, Jan. 1972, 
pp. 23-37. 

16. Richter, T. A. E.; Warman, M.; and Sowin- 
ski, E., “NMR Spectral Atlas of Aromatic Ni- 
tro Compounds,” Technical Report 3529, Ex¬ 
plosives Laboratory, Feltman Research Labora¬ 
tories, Picatinny Arsenal, Dover, New Jersey, 
November 1967. 

17. Hogan, V. D., and Richter, T. A. E., “A 
New Convenient Tool For Identifying Compos¬ 
ite Explosives: Proton Magnetic Resonance 
Fingerprinting,” Technical Report 4790, Explo¬ 
sives Division, Feltman Research Laboratories, 
Picatinny Arsonal, Dover, New Jersey, June 
1975. 

18. Hogan, V. D., “Proton Magnetic Resonance 
Fingerprinting for Identification of Composite 
Explosives and Explosive Materials. Part II,” 
Technical Report ARLCO-TR-80047, US 
Army Armament Research and Development 
Command, Large Caliber Weapon Systems 
Laboratory, Dover, New Jersey, February 
1981. 


106 


THE USE OF MULTIPLE DETECTION IN THE GAS CHROMATOGRAPHIC 
ANALYSIS OF ORGANIC NITRO COMPOUNDS AND EXPLOSIVES 

(GC-ECD/PID) 


I. S. Krull*, M. Swartz, and K-H. Xie 
Institute of Chemical Analysis and 
Department of Chemistry 
Northeastern University 
360 Huntington Avenue 
Boston, Mass. 02115 
and 

J. N. Driscoll 
HNU Systems, Inc. 

30 Ossipee Road 
Newton, Mass. 02164 


Abstract. The trace organic analysis for nitro derivatives and explosives has 
traditionally been hampered in gas chromatography by a lack of suitably selective 
and sensitive detectors. Except for the mass spectrometer, and perhaps the Ther¬ 
mal Energy Analyzer, most other GC detectors are not suitably selective for nitro 
compounds to provide unambiguous identification of trace amounts in complex 
sample matrices. In recent years, numerous workers have applied a combination of 
detectors, in series or parallel, for improved compound identifications. We have 
now utilized a parallel arrangement of electron capture detection (ECD) and 
photoionization detection (PID), together with certain Permabond GC packing 
materials, for the improved resolution and specific identification (speciation) of 
numerous organic/nitro compounds and explosives. The combination of 
GC-ECD/PID for nitro derivatives provides relative response factors vs a com¬ 
mon internal standard, as well as ratios of ECD/PID relative response factors that 
are often unique for individual nitro compounds. We have now applied these 
analytical methods to a wide variety of nitro derivatives, including: mono-nitro 
toluenes; dinitrotoluenes, dinitrobenzenes, nitro aliphatics, nitro-PAHs, poly¬ 
cyclic aromatic hydrocarbons (PAHs), and various explosive compounds. Separa¬ 
tions of mixtures of the aromatic nitro derivatives, PAHs, nitro-PAHs, or explo¬ 
sives, were obtained using glass packed columns of Permabond Methyl Silicone, 
Permabond PEG 20M, and/or Permabond PAH packings. In most instances, tem¬ 
perature programmed separations were interfaced with fixed ratio splitting of the 
GC effluent to the ECD and PID detectors. The combination of ECD and PID 
provides for vastly different response factors in comparing the PAHs and 
nitro-PAHs, so that the resultant normalized relative response factors for the ratio 
of ECD/PID become vastly different on an absolute scale. Thus, in certain cases, 
PAHs and their nitro-PAH derivatives can exhibit 3-7 orders of magnitude differ¬ 
ences in their relative response factors for ECD/PID ratios. 

The use of combined ECD/PID ratios and relative response factors in GC analy¬ 
ses for organic nitro compounds and related explosives provides a unique method 
of utilizing relatively available detectors for improved analyte identification and 
specificity at little added overall cost. These methods are directly applicable to en¬ 
vironmental samples containing trace amounts of nitro derivatives and/or explo¬ 
sives. Gas chromatography-multiple detection is a very viable and valid method 


107 


for the trace analysis of these types of compounds. (This work was supported, in 
part, by an NIH Biomedical Research Support Grant No. RR07143 to Northeast¬ 
ern University, Department of Health and Human Services.) 


SUMMARY 

Combined detectors in gas chromatography 
(GC), such as electron capture detection (ECD) 
and photoionization detection (PID) have now 
been utilized for improved qualitative identifica¬ 
tion of a wide variety of organic nitro compounds. 
GC retention times together with relative response 
factors and ratios of ECD/PID response factors 
are reported for this class of derivatives. Mini¬ 
mum limits of detection on ECD and PID, relative 
response factors, and ratios of relative response 
factors (RRF/RRF) are derived from mixtures of 
organic nitro compounds separated via GC with 
temperature programming. A new type of GC 
packing material, the covalently bonded Perma- 
bond supports, are utilized for most of these 
studies with combined ECD/PID detection in GC. 
Organic nitro compounds are of considerable in¬ 
terest because they are widely distributed as en¬ 
vironmental pollutants and toxicants, as well as 
being found in explosives, veterinary products, 
pharmaceuticals, perfumes, cosmetics, propel¬ 
lants, industrial raw materials, and finished con¬ 
sumer products. 

INTRODUCTION 

Organic nitro derivatives are a class of com¬ 
pounds that are of current analytical and toxico¬ 
logical interest due to many reasons. A large num¬ 
ber of aliphatic and aromatic nitro compounds, 
such as those in Figures 1 and 2, have to different 
degrees, already been found in various environ¬ 
mental, industrial, biological, and chemical sam¬ 
ples. At times, such compounds are formed within 
such samples from suitable precursors, and at 
times, they are initially present as contaminants 
from other sources [Scheutzle et at. (1982), Pitts et 
al. (1979, 1978), Rosenkranz et al. (1980), Lofroth 
et al. (1980), Rosseel and Bogaert (1979), Yap et 
al. (1978), Krull and Camp (1980)]. It has also be¬ 
come of considerable concern that a very large 
number of nitro compounds, especially the poly¬ 
aromatic derivatives, display varying degrees of 
mutagenicity and/or carcinogenicity [Cohen et al. 
(1976), Wang et al. (1975), Wang et al. (1978), 
Won et al. (1976), Griswold et al. (1968), Pitts et 
al. (1977), Khudoley et al. (1981), Goodall and 
Kennedy (1976), Whong et al. (1980)]. Many nitro 
compounds are used as drugs, veterinary prod¬ 


ucts, cosmetic ingredients, perfumes and fra¬ 
grances, explosives and propellants, agricultural 
chemicals, industrial raw materials and interme¬ 
diates, bactericides, and other consumer/indus¬ 
trial products. Because of their wide chemical di¬ 
versity and widespread distribution via consumer 
and industrial products, as well as the fact that 
many are formed environmentally, it has become 
obvious that many nitro compounds have become 
widespread environmental pollutants and/or con¬ 
taminants. There has therefore developed an in¬ 
tense interest in the development of trace methods 
of analysis and speciation for various nitro deriva¬ 
tives, including the use of gas chromatography 
(GC) with a variety of detectors, high perform¬ 
ance liquid chromatography (HPLC) with as¬ 
sorted detectors, as well as direct analysis via mass 
spectrometry (MS) and related instrumental tech¬ 
niques [Demko (1979), Mourey and Siggia (1979), 
Takagi et al. (1981), Ramdahl et al. (1982), 
Langhorst (1981)]. In the past, most trace analyses 
for various nitro compounds present in complex 
sample matrices, involved the use of GC with a 
variety of selective and/or general detectors, such 
as flame ionization detection (FID), electron cap¬ 
ture detection (ECD), alkali flame ionization de¬ 
tection (AFID), Thermal Energy Analysis (TEA), 
Coulson electrolytic conductivity detection 
(CECD), and others. Within the past few years, a 
very large number of HPLC based analyses for ni¬ 
tro compounds have been described, making use 
of electrochemical detection (EC), electron cap¬ 
ture detection (ECD), photoconductivity detection 
(PCD), Thermal Energy Analysis (TEA), and oth¬ 
ers [Krull and Camp (1980), Krull (1983), Krull et 
al. (1981), Jacobs and Kissinger (1982), Bratin et 
al. (1981)]. 

Most trace analyses for organic nitro com¬ 
pounds still rely on GC-detector methods, in part 
because of the lower detection limits possible and 
the general widespread availability of the instru¬ 
mentation required. Of late, there has been a dis¬ 
tinct interest in the application of photoionization 
detection (PID) for a wide variety of trace organic 
analyses. At the same time, there is considerable 
interest in combining the PID with other selective 
and/or general GC detectors for improved analyte 
identification in trace analysis [Driscoll et al. 
(1982), Driscoll et al. (1980), Jaramillo and 


108 


Driscoll (1979), Driscoll et al. (1978a), Driscoll et 
al. (1978b), McKinley et al. (1982), Conron et al. 
(1982), Langhorst and Nestrick (1979)]. The use of 
more than one detector response per analyte of in¬ 
terest has recently gained widespread popularity 
and acceptance as a valid analytical method for 
improving the qualitative identification of individ¬ 
ual GC analytes [Gagliardi et al. (1981), Parliment 
(1982), McCarthy et al. (1981), Bachmann et al. 
(1977), Poy (1979), Bjorseth and Eklund (1979), 
Cox and Earp (1982)]. In most applications, the 
combination of a general and selective or selective 
and selective defector for organic nitro com¬ 
pounds should provide more compound specific¬ 
ity and identification than the use of two detectors 
that both respond to about the same extent with 
such materials. Thus, the use of FID and ECD for 
nitro compounds would not be expected to pro¬ 
vide any unusual degree of analyte specificity, be¬ 
cause most/all aliphatic or aromatic nitro com¬ 
pounds would provide about the same degree of 
response on both FID, or ECD. On the other 
hand, a combination of FID with PID, or ECD 
with PID, or all three detectors simultaneously, 
should provide an unusual degree of compound 
identification and specificity. This assumes, of 
course, that the PID will indeed demonstrate more 
selectivity for aliphatic vs aromatic nitro deriva¬ 
tives than either the FID or ECD. This assumption 
has been supported by the earlier work of Driscoll 
et al. (1978b). With regard to the application of 
the PID for nitro derivatives in general, this has 
been described for a very limited number of vari¬ 
ety of such compounds by Langhorst (1981). This 
paper described the PID relative responses vs ben¬ 
zene for nitrobenzene, 2,4-dinitrotoluene, 4-ni- 
trophenol, and 2,4-dinitrophenol, but there was 
no mention of any aliphatic nitro derivatives. 

We describe here the simultaneous application 
of both ECD and PID for a large number of ali¬ 
phatic and aromatic nitro derivatives, includ¬ 
ing: nitropentane, nitrocyclohexane, o-, m-, and 
p-nitrotoluene, 2,3-, 2,4-, 2,6-, and 3,4-dinitro- 
toluene, o-, m-, and p-dinitrobenzene, polycyclic 
aromatic hydrocarbons and their mono-nitro de¬ 
rivatives (Figures 1 and 2). PAHs and ni- 
tro-PAHS are of considerable interest as environ¬ 
mental air and water pollutants, and because of 
their demonstrated carcinogenicity and/or muta¬ 
genicity in mammalian systems. All of these 
GC-ECD/PID analyses have been performed 
with either Ultrabond 20M, Permabond Methyl 
Silicone, and/or Permabond PEG 20M packing 


materials in glass packed columns. Permabond 
packing materials have recently gained widespread 
attention because of their very light loading, 
covalent attachment of the liquid (organic) phase 
to the solid, inert support, and their general high 
temperature stability [Langhorst (1981), Lang¬ 
horst and Nestrick (1979)]. We describe here the 
GC separation conditions utilized, detector oper¬ 
ating parameters, retention times and resolution 
factors, minimum limits of detection via 
ECD/PID, linearity ranges of response, normal¬ 
ized response factors on various detectors, and re¬ 
lated, appropriate analytical parameters of inter¬ 
est for these nitro derivatives. All of this work has, 
thus far, involved the use of commercially avail¬ 
able chemical standards, but the final analytical 
and detection methods and results should be di¬ 
rectly applicable to real world samples for these 
and other nitro derivatives. It is the intention of 
this work that such methods will indeed be even¬ 
tually applied in other laboratories to practical en¬ 
vironmental, industrial, biological, and toxico¬ 
logical sample matrices of interest to workers in 
such fields. 





p-NITROTOLUENE 






no 2 


o-DINITROCENZENE 



NITROCYCLOHEXANE 


m-DINITROEENZENE 


CH 3 (CH 2 > 4 N° 2 

NITROPENTANE 


p-DINITROBENZENE 

Figure 1. Aliphatic and aromatic nitro derivatives studied via 
GC-ECD/PID with Permabond column packings. 


109 




INDAN 



5-NITROINDAN 





PYRENE 

Figure 2. Polycyclic aromatic hydrocarbons (PAHs) and 
nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) studied 
via GC-ECD/PID with Permabond column packings. 



EXPERIMENTAL 

Equipment 

These results were obtained using a Varian 
Model 3700 gas chromatograph (Varian Asso¬ 
ciates, Inc., Palo Alto, Calif.), equipped with con¬ 
ventional Varian FID and ECD detectors. A sepa¬ 
rate PID unit was mounted external to the main 
GC oven, on top of the GC itself, with external 
heating tape applied to the interface, in order to 
prevent any condensation of the GC effluents af¬ 
ter their exit from the column oven. The PID was 
obtained from HNU Systems, Inc., Model No. 
Pl-51-01 (HNU Systems, Inc., Newton, Mass.). 
For dual detection in parallel, viz., ECD/PID, it 
was necessary to construct a special, glass-lined, 
metal tee splitter using / 6 -in x 0.5-mm i.d. 
glass-lined stainless steel tubing (Scientific Glass 
Engineering, Inc., Austin, Texas). Additional 
parts for this all glass-lined interface between the 
end of the GC column and the two detectors in¬ 


clude drilled through Swagelok reducing union, 
/ g -in x / b - in, (Cambridge Valve & Fitting, Inc., 
Billerica, Mass.), and Varian detector inlets 
(Varian Corp.). A Weller Mini-Shop variable 
speed cutter with a diamond cutting wheel (Jensen 
Tools, Tempe, Arizona) was used to cut the 
glass-lined metal tubing. This fixed ratio splitter 
was monitored before, during, and after various 
days’ analyses, to ensure that the actual eluent 
split to each detector was reproducible and well 
defined. Temperature programming does not 
change the eluent split ratio using this type of a 
fixed ratio GC splitter. 

For those studies involving only nitropentane, 
nitrocyclohexane, o-nitro-toluene, and 2,6-dini- 
trotoluene in the analyte mixture, a GC column 
packing of Ultrabond 20M (RFR Corp., Hope, 
R.I.) was used, in a packed glass column, 6—ft x 
2.0-mm i.d. All of the aromatic nitro derivatives, 
PAHs, and nitro-PAHs were eventually analyzed 
on two separate GC columns with slightly differ¬ 
ent temperature programming conditions. The 
first such column was a glass packed column 6—ft 
x 2.0-mm i.d., of Permabond Methyl Silicone 
(HNU Systems, Inc.). The second GC column in 
this series was a glass packed column 6—ft x 
2.0-mm i.d., of Permabond PEG 20M (HNU Sys¬ 
tems, Inc.). Specific GC separation conditions for 
each of these columns are indicated below (Results 
and Discussion). The support gases used for the 
GC carrier gas and detector support gases (FID) 
were obtained from Matheson Gas Co. (East 
Rutherford, N.J.). All GC-detector chromato¬ 
grams were recorded on a Linear dual pen record¬ 
er (Linear Instruments Corp., Irvine, Calif.) at a 
chart speed of 1 cm/min and an output of 1 mV. 

Reagents and Solvents 

Individual nitro compounds, PAHs, or ni¬ 
tro-PAHs, were obtained from a variety of com¬ 
mercial sources, including: Pfaltz & Bauer, Inc. 
(Stamford, Conn.), Aldrich Chemical Co. (Mil¬ 
waukee, Wise.), Chem Service (West Chester, 
Penna.), MCB Chemicals, Inc. (Medford, Mass.), 
or Fisher Scientific, Inc. (Fair Lawn, N.J.). All of 
the solvents used to prepare the standard solutions 
for GC analyses were HPLC grade, dis- 
tilled-in-glass, and were obtained from commer¬ 
cial suppliers, such as: J. T. Baker Chemical Co. 
(Phillipsburg, N.J.) or MCB Omnisolv (Doe & 
Ingalls, Inc. (Medford, Mass.). Chemicals and 
solvents were not purified further, but were used 
directly as received from the supplier. 


110 





















Methods 

Individual stock solutions of each nitro deriva¬ 
tive or mixtures of nitro compounds, PAHs, or ni- 
tro-PAHs were prepared in volumetric flasks by 
carefully weighing or measuring out an initial 
amount of each standard. The solvents used to 
dissolve such chemical standards were chosen so 
that they would be compatible with the particular 
GC detectors being used. In most cases, acetone 
alone or a 1:1 (v/v) mixture of hexane:acetone was 
satisfactory for such standard solutions. Solutions 
once prepared were kept in the dark in the refrig¬ 
erator, and if a question arose with regard to 
changes in concentration levels, then fresh stand¬ 
ard solutions were prepared the same day as the 
analytical studies involved. All standard solutions 
were prepared with an internal standard, o-nitro- 
toluene, added at the same time as the compounds 
of interest. Injections onto the GC were made with 
a Hamilton Model No. 701N syringe (Hamilton 
Company, Reno, Nevada), and these were gener¬ 
ally less than 2 ul injections. Solvent blanks were 
always injected before and after the standard solu¬ 
tions of analytes, to ensure that any peaks being 
observed were not derived from the solvent itself 
or any impurities therein. All injections of stand¬ 
ards and solvent blanks were performed at least in 
duplicate, under identical GC-detector operating 
conditions. 

The nitroaromatics and nitro-PAHs were con¬ 
verted to their expected amino derivatives using a 
tin/HCL reduction method. This consisted of 
adding lg of the nitro compound to 2g of gran¬ 
ulated tin in a small flask. The flask was con¬ 
nected to a reflux condenser, and 20 ml of 10% 
HC1 was added in small portions, with vigorous 
shaking after each addition. The mixture was then 
warmed on a steam bath for 10 mins, the solution 
was decanted while hot, and sufficient 40% sodi¬ 
um hyroxide solution was added to dissolve the tin 
hydroxide. The solution was then extracted sever¬ 
al times with 10ml portions of ethyl ether. The 
ether extracts were then combined, dried over 
anhydrous sodium sulfate, filtered from the dry¬ 
ing agent, and this final solution was either direct¬ 
ly injected onto the GC or first diluted with addi¬ 
tional ether before injection. 

RESULTS AND DISCUSSION 

All of the analytical results presented here have 
been obtained using packed glass columns, mostly 
with Permabond type packing materials, and in 
most instances using temperature programming. 


Capillary columns have always been an alternative 
approach, but this would have required the use of 
somewhat modified detectors, in order to fully 
utilize the efficiencies inherent within capillary 
columns. We have not found it necessary to utilize 
capillary columns for these studies, since im¬ 
proved analyte specificity has been realized with 
conventional packed columns together with the 
different selectivities inherent in ECD and PID de¬ 
tection methods. Combined detector responses, 
normalized relative response factors (RRFs), and 
ratios of such relative response factors 
(ECD/PID), have provided greatly improved se¬ 
lectivity over single detector methods in conven¬ 
tional GC. For unusually complex sample mix¬ 
tures, capillary column resolutions may prove a 
necessity, but this would then require suitable 
modifications in the dimensions of the conven¬ 
tional GC detectors employed. 

In all of the PID analyses, a 10.2 eV lamp has 
been used, in part becuase of its greater light in¬ 
tensity at this power level. Since other, higher and 
lower, eV lamps are commercially available, it 
should be possible in future work to obtain addi¬ 
tional selectivity differences for these same nitro 
derivatives or PAHs. Such data, together with the 
same ECD responses described below, would then 
provide additional analyte identification and se¬ 
lectivity. Clearly, the ability to vary the power (en¬ 
ergy) level of the commercial PID unit, together 
with conventional ECD applications, offers the 
analyst an unusual degree of compound/analyte 
selectivity and specificity. 

We have compared the selectivity possible for 
equi-molar amounts of four typical organic nitro 
compounds, viz., nitropentane, nitrocyclohexane, 
o-nitrotoluene, and 2,6,-dinitrotoluene, Figure 1, 
using FID, ECD, and PID. Figure 3 illustrates the 
GC-FID/PID chromatograms for these four 
standards, with the amounts of each reaching the 
detectors as indicated. Specific GC-detector con¬ 
ditions are indicated in Figure 3 and above (Ex¬ 
perimental). As expected, the FID responses are 
approximately equal for equi-molar amounts of 
organic nitro compounds, on a general type detec¬ 
tor. However, the PID responses are vastly differ¬ 
ent, especially when comparing aliphatic nitros vs 
aromatic nitro compounds. Even at the low 
ug/compound levels injected here, neither of the 
aliphatic nitro derivatives appear on the PID. The 
differences in sensitivities for organic nitro com¬ 
pounds must be due to inherent differences in the 
ionization potentials of these compounds, since 


111 


this is the physical basis for the selectivities possi¬ 
ble with the PID. The absolute amounts of each 
compound reaching the PID are in the 5-10ug 
range. The GC-ECD analysis for these same four 
organic nitro compounds showed, as expected, ap¬ 
proximately equal responses for the mono-nitro 
materials for equi-molar amounts reaching the 
ECD, and about a doubling of the response for 
the 2,6-dinitrotoluene isomer. Thus, of all three 
detectors initially studied here, only the PID 
shows a high degree of selectivity for aliphatic and 
aromatic nitro derivatives. 

With regard to the minimum detection limits 
(MDLs) for these same four nitro materials, and 
thus indirectly the relative response factors 
(RRFs), this data is presented in Table 1. These 
MDLs were determined using a signal/noise ratio 
of approximately 2:1 with lower and lower 
amounts of each nitro compound being injected 



Figure 3. GC-FID/PID chromatograms of four standard 
nitro organics using a 6-ft x 2.0-mm i.d. packed glass column 
of Ultrabond 20M, with temperature programming from 50°C 
(2 mins) to 180°C at 10°C/min, with a final hold at 180°C until 
elution of fourth analyte. Injector and detector temperatures 
were 230°C-250°C. Carrier gas flow rate, nitrogen, was about 
40 ml/min, with a 70/30 split between F1D/P1D. Amounts in¬ 
dicated are those reaching each detector. 


and detected. As initially suggested in Figure 3, 
the MDLs via FID and ECD are approximately 
equal within each detector category. However, the 
PID MDLs are vastly different from one another. 
This is a direct reflection of the differences in 
RRFs for these four nitro derivatives on the PID, 
as discussed further below. 

Table 1: MINIMUM DETECTION LIMITS FOR FOUR 
TYPICAL NITRO COMPOUNDS <ng) a ON 
THREE TYPICAL GC DETECTORS 


Compound 

FID 

Detector Type 

PID ECD 

N1TROPENTANE 

1.06 

0.00b 

0.14 

NITROCYCLOHEXANE 

1.04 

0.00b 

0.03 

O-NITROTOLUENE 

0.93 

0.40 

0.03 

2,6-DINITROTOLUENE 

1.13 

2.80 

0.01 


a. GC conditions used a 6-ft x 2.0-mm i.d. packed glass col¬ 
umn of Ultrabond 20M operated from 50°C to 180°C at 
10°C/min with nitrogen carrier gas flow rate of 40 ml/min 
total. 

b. 0.00 indicates that there was no apparent response for these 
compounds at any level below 1 ug injected on-column via 
PID detection. 

Separations of Nitro Derivatives on Permabond 
Packing Materials 

All of the remaining data for normalized rela¬ 
tive response factors on ECD and PID, as well as 
the ratios of RRFs for ECD/PID, for nitro aro¬ 
matics, PAHs, and nitro-PAHs, have been deter¬ 
mined using either the Permabond Methyl Silicone 
or Permabond PEG 20M packing materials. Fig¬ 
ure 4 is a GC-ECD/PID set of chromatograms for 
the three mono-nitrotoluene isomers (o-, m-, and 
p-), together with the specific GC-detector oper¬ 
ating conditions and parameters. The amounts in¬ 
dicated are those going to each detector, taking in¬ 
to account the known/determined split ratio of 
the GC effluent before the detectors. Knowing the 
absolute split ratio throughout the temperature 
programmed analysis, the absolute amounts of 
each compound injected, and the determined peak 
heights at each recorder/detector attenuation set¬ 
ting, it was possible to calculate relative factors 
for individual compounds. We have taken o-ni- 
trotoluene as the reference compound, and all oth¬ 
er ECD and PID responses are then referenced to 
o-nitrotoluene as being 1.00 on each detector. 
Thus, relative response factors, RRFs, are deter¬ 
mined directly by measuring peak heights and ab¬ 
solute amounts of each compound reaching that 
detector. The ratio of peak heights (mm/cm) di¬ 
vided by the number of ng or ug reaching that 


112 





























ECD RESPONSE (TIME, MINUTES) 

0 2 4 6 8 10 

I_I_ I I _I_I_I_ I I l I 



PID RESPONSE (TIME, MINUTES) 

Figure 4. GC-ECD/PID chromatograms of the three 
mono-nitrotoluene isomers using a 6-ft x 2.0-mm i.d. packed 
glass column of Permabond Methyl Silicone operated from 
50°C to 180°C with temperature programming of 10°C/min. 
Nitrogen carrier gas flow rate of about 30-40 ml/min with a 
split ratio between the PID/ECD detectors of about 40/60. 
Amounts indicated are those reaching each detector. 


same detector then provides us with normalized 
response factors. Normalized relative response 
factors are simply obtained by using the relative 
response factor for 0-nitrotoluene as 1.00 and ref¬ 
erencing all other RRFs to that value. This is the 
origin of our determinations of normalized RRFs. 
Quite naturally, such calculations are based on de¬ 
tector responses measured or corrected at the same 
attenuation settings on detector amplifier and rec¬ 
order. 

Table 2 summarizes the RRFs on ECD and PID 
for the above mono-nitrotoluenes, as well as a 
variety of other dinitrotoluene isomers and dini¬ 
trobenzene isomers, as described further below. 
For these two detectors, the RRFs within each 
group of aromatic nitro derivatives are about the 
same, and therefore the ratio of RRFs for 
ECD/PID are also about the same for each group. 
Thus, for similar aromatic nitro isomers, neither 
the PID nor the ECD provide greatly improved se¬ 
lectivity over the FID. However, Table 2 demon¬ 
strates that wherein one compares the ratios of 
RRFs for ECD/PID between these three classes of 
aromatic nitro derivatives, this does offer a unique 
handle for characterizing each separate class. That 
is, the mono-nitrotoluenes are clearly distinguish¬ 
able from the dinitrobenzenes, since these do not 
show any response at these levels on the PID. For 
the dinitrotoluenes, their ECD/PID ratios of 
RRFs are again quite different from the other two 
groups of nitroaromatics in Table 2. Although this 
approach of using ratios of detector responses, af¬ 
ter normalization, has been suggested by others 
for other classes of organic compounds, its value 
and analytical utility has rarely been as clearly 
demonstrated as for the organic nitro compounds, 
Table 2. 

For the GC-ECD/PID analyses of all other 
groups of nitro aromatics, PAHs, or nitro-PAHs, 
we have utilized o-nitrotoluene as an internal 
standard always present in the mixtures being ana¬ 
lyzed. Figure 5 is a superimposed combination of 
two separately obtained chromatograms, but both 
being obtained under identical GC conditions. Be¬ 
cause the ECD and PID detector responses to the 
dinitrotoluene isomers were so very different, it 
was not possible, with the fixed ratio splitter used, 
to obtain both ECD and PID chromatograms via 
a single injection of these compounds. With a 
variable ratio splitter in place of the fixed ratio 
one, this problem could have been overcome and 
both chromatograms could have been obtained via 
a single injection. However, variable ratio splitters 


113 






















Table 2. RELATIVE RESPONSE FACTORS FOR N1TRO AROMATICS VIA GC-ECD/PII> a 


Compound 

PID 

Relative Response Factors (RRFsK 

ECD 

ECD/PID^ 

O-NITROTOLUENE 

1.00 


1.00 

1.00 

m-NITROTOLUENE 

1.06 


1.11 

1.05 

p-NITROTOLUENE 

1.56 


1.06 

0.68 

2,3-DINITROTOLUENE 

2.92 x 

10-2 

5.44 

186.3 

2,4-DINITROTOLUENE 

9.00 X 

10-2 

4.86 

540 

2,6-DIN ITROTOLUENE 

2.46 x 

10-2 

5.47 

222.4 

3,4-DINlTROTOLUENE 

1.78 x 

10-2 

4.94 

277.5 

O-DINITROBENZENE 

_e 


4.86 

-e 

m-DINITROBENZENE 

-e 


3.31 

_e 

p-Dl NITROBENZENE 

_e 


5.81 

-e 


a. Data was obtained using identical GC conditions for both ECD/PID as indicated in Figure 4. Amounts of each compound 
reaching each detector was determined knowing amounts injected with determined split ratios on each day’s runs. 

b. GC conditions employed a 6-ft x 2.0-mm i.d. packed glass column of Permabond Methyl Silicone with temperature program¬ 
ming. 

c. Relative response factors (RRFs) were obtained by measuring peak heights (cm) and dividing by absolute amount reaching that 
detector (ng), to obtain a response factor as cm/ng for each compound. O-Nitrotoluene was assigned an arbitrary value of 1.00 
cm/ng, and all other response factors were calculated relative to o-nitrotoluene to obtain final RRFs. 

d. ECD/PID ratios were obtained by dividing RRFs via ECD and P1D for each compound, but using on both ECD and PID the 
o-nitrotoluene response as 1.00. 

e. There was no measurable response below ug amounts for any of the dinitrobenzenes on the PID. 


do not provide fixed splitting factors, at a given 
setting, throughout a temperature programmed 
GC analysis. The specific GC-detector conditions 
and amounts reaching each detector are indicated. 
Figure 5. In Figure 5, there is a single peak for 
both 2,3- and 2,4-dinitrotoluene derivatives, 
which were not successfully resolved on this pack¬ 
ing material. However, relative response factors 
were obtained by separate injections of each of 
these two isomers, together with the internal 
standard, O-nitrotoluene. An improved resolution 
of all for dinitrotoluene isomers involved here was 
eventually obtained, as indicated below. The indi¬ 
vidual RRFs and ratios of ECD/PID RRFs for 
these four dinitrotoluenes are indicated in Table 2, 
and these have been compared and discussed, as 
above. 

The minimum detection limits for the mono-ni- 
trotoluenes, dinitrotoluenes, and dinitrobenzenes, 
on both ECD and PID, are indicated in Table 3, 
using GC conditions described above, Figures 4 
and 5. In each instance, the MDLs via ECD are or¬ 
ders of magnitude lower than via PID. It is gener¬ 
ally realized that for organic nitro compounds, de¬ 
tection limits will always be lower on the ECD 
than the PID. However, compound identification 
and detector selectivity will generally be better via 
the PID rather than the ECD. In deciding which 
detector is to be most useful for organic nitro 
compound analysis, one must first decide whether 
it is detectability or selectivity that is of greater 
concern. 


Table 3. MINIMUM DETECTION LIMITS FOR ISO¬ 
MERIC NITRO DERIVATIVES VIA GC-ECD/ 
PID a 


Compound 

Detector Type 


ECD (ng) 

PID 

o-NITROTOLUENE 

0.022 

5.95 ng 

m-NITROTOLUENE 

0.020 

5.61 ng 

p-NITROTOLUENE 

0.021 

3.81 ng 

2,3-DIN ITROTOLUENE 

0.003 

0.05 ug 

2,4-DINITROTOLUENE 

0.003 

0.162 ug 

2,6-DIN ITROTOLUENE 

0.003 

0.059 ug 

3,4-DIN ITROTOLUENE 

0.003 

0.082 ug 

o-DINITROBENZENE 

0.045 

_b 

m-DINITROBENZENE 

0.066 

_b 

p-DINITROBENZENE 

0.046 

-b 


a. GC conditions used a 6-ft x 2-mm i.d. glass packed column 
of Permabond methyl silicone operated from 50-180°C at 
10°C/min with carrier gas flow rate of 35-40 ml/min. De¬ 
tection limits were determined by injecting lower and lower 
absolute amounts of each compound using a final sig¬ 
nal/noise ratio of 2/1 at the lowest attenuations possible or 
feasible. 

b. Indicates that there was no apparent response for these 
compounds at any level below 1 ug injected on-column via 
PID detection. 

The Permabond Methyl Silicone packing mate¬ 
rial has also been utilized for the resolution and 
detection via ECD/PID of several typical polycy¬ 
clic aromatic hydrocarbons (PAHs) and their ni- 
tro-derivatives (nitro-PAHs). Figure 6 is a 
GC-PID chromatogram of five PAHs together 
with o-nitrotoluene as the internal standard, with 
the amounts indicated going to the PID. Specific 


114 




ECD RESPONSE (time, minutes) 

o 2 4 6 8 10 12 14 16 

I - 1 - 1 - 1 _ I _ I _ I _ I I I I I I I I I I 



PID RESPONSE (TIME, MINUTES) 

Figure 5. GC-ECD and GC-PID chromatograms for mixture 
of o-nitrotoluene and three dinitrotoluene isomers. The indi¬ 
vidual GC chromatograms were superimposed on top of one 
another for ease of comparison between the two detectors. GC 
conditions in each case used a packed glass column, 6—ft x 
2.0-mm i.d., of Permabond Methyl Silicone, operated from 
50°C to 180°C at 10°C/min, with a nitrogen carrier gas flow 
rate of 40 ml/min. Amounts indicated are those reaching each 
detector. GC eluent split ratio between PID/ECD was 40/60. 



Figure 6. GC-PID chromatogram of a mixture of polycyclic 
aromatic hydrocarbons with o-nitrotoluene as internal stand¬ 
ard. GC conditions used a 6—ft x 2.0-mm i.d., packed glass 
column of Permabond Methyl Silicone operated from 40°C to 
225 °C at 15°C/min with temperature programming. Nitrogen 
carrier gas flow rate of 15 ml/min to PID. 

GC conditions for this determination are indicated 
in the Figure. Although naphthalene is not base¬ 
line resolved from o-nitrotoluene, the relative 
peak heights can be accurately determined, togeth¬ 
er with relative response factors for all of the 
PAHs involved. As expected, PAHs respond con¬ 
siderably better on the PID than on the ECD, and 
these relative response factors have been summa¬ 
rized in Table 4 for both the PAHs and ni- 
tro-PAHs of interest here. 


Table 4. RELATIV E RESPONSE FACTORS (RRFs) AND ECD/PID RATIOS FOR PAHs AND THEIR NITRO-PAH ANA¬ 
LOGS'* 


Compounds 

ECD 

PID 

ECD/PIDh 

o-NITROTOLUENE 

1.00 

1.00 

1.00 

INDAN 

7.18 x 10 - s 

5.4 x 10-1 

1.34 X 10-4 

5-NITROlNDAN 

2.32 

1.18 

1.97 

NAPHTHALENE 

8.01 x 10-6 

2.86 x 10-1 

2.80 x 10-5 

2-N1TRONAPHTHALENE 

4.73 

1.25 

3.78 

FLUORENE 

-c 

7.62 x 10-i 

-c 

2-NITROFLUORENE 

3.48 

7.5 x 10-1 

4.64 

ANTHRACENE 

6.73 x 10-- 1 

5.20 x 10-1 

8.83 x 10-3 

9-N1TROANTHRACENE 

2.50 

1.38 

1.81 

PYRENE 

1.53 x 10-2 

3.88 x 10-1 

3.94 x 10-2 


115 










































Table 4. RELATIVE RESPONSE FACTORS (RRFs) AND ECD/PID RATIOS FOR PAHs AND THEIR NITRO-PAH ANA- 


LOGS 8 —Cont. 




Compounds 

ECD 

PID 

ECD/PID'’ 

3-NITROPYRENE 

2.18 

3.70 x 10-1 

5.89 

o-NITROTOLUENE 

1.00 

1.00 

1.00 


a. GC conditions used a 6-ft x 2.0-mm i.d. packed glass column of Permabond Methyl Silicone operated with temperature pro¬ 
gramming from 40°C to 225 °C at 15°C/min with nitrogen carrier gas flow rate of 15 ml/min. 

b. All calculations were done using peak heights and not peak areas. ECD and PID responses were first normalized to that of o-ni- 
trotoluene at 1.00 (cm/ng) knowing amounts of each compound injected, detector attenuations, and peak heights obtained 
(cm). Analyzed as mixtures of PAHs or nitro-PAHs with o-nitrotoluene present as internal standard. 

c. It was not possible to obtain any measurable ECD response for fluorene at ug levels or above reaching the ECD. 


Figure 7 is a combination of two superimposed 
GC-ECD and GC-PID chromatograms for a mix¬ 
ture of five different nitro-PAHs with o-nitro¬ 
toluene as the internal standard. These two chro¬ 
matograms were obtained separately, using identi¬ 
cal GC conditions, but with different levels of the 
nitro-PAHs injected as a function of the detector 
in use. The final two chromatograms have then 
been purposely superimposed in order to be able 
to make direct detector comparisons more appar¬ 
ent. GC conditions are indicated in Figure 7 and 
above (Experimental). Although 2-nitrofluorene 
and 9-nitroanthracene have not been baseline re¬ 
solved in Figure 7, separate injections of each of 
these alone enabled the determination of relative 
response factors vs o-nitrotoluene for each detec¬ 
tor. 

A summary of the PAH and nitro-PAH relative 
response factors for ECD and PID is indicated in 
Table 4, wherein these have been normalized and 
related to o-nitrotoluene as the base response of 
1.00 on both detectors. This provides the data in 
the first two columns, and when the ratio of these 
normalized RRFs are taken, the final column 
headed ECD/PID can be obtained, Table 4. It is 
immediately apparent that the PAHs respond or¬ 
ders of magnitude better on the PID than on the 
ECD, and that the nitro-PAHs have responses on 
the ECD that are, in general, an order of magni¬ 
tude or so better (more intense) than on the PID. 


That is, these two classes of compounds respond 
in opposite directions, with regard to sensitivity, 
for these two particular detectors. When the ratios 
of RRFs for ECD/PID, column three in Table 4, 
are calculated, the overall differences between the 
PAHs and their nitro-PAH derivatives can be sev¬ 
eral orders of magnitude. Table 5 makes this last 
comparison directly, wherein for each pair of 
PAH and nitro-PAH, their respective PID/PID 
and ECD/ECD ratios are presented in columns 1 
and 2. The final column in Table 5, viz., the re¬ 
spective ECD/PID-ECD/PID ratios from Table 4 
for each pair of PAH and nitro-PAH are indi¬ 
cated. That is, the ECD/PID ratio from Table 4 
for a particular PAH is divided by the analogous 
ECD/PID ratio for its direct nitro-PAH analog 
(indan/5-nitroindan). It is just this final column 
of Table 5 that is of most interest, because it for 
the first time indicates that ECD/PID ratios can 
be 3 to 6 orders of magnitude different between 
any given PAH and its corresponding nitro-PAH. 
This suggests an unusually high degree of selectiv¬ 
ity for any particular PAH and its nitro derivative 
via GC-ECD/PID relative response factors and 
their derived ratios, Table 5. Since many environ¬ 
mental samples have already been shown to con¬ 
tain PAHs together with nitro-PAHs, this ap¬ 
proach should provide a new method of confirm¬ 
ing the class of compounds that an unknown GC 
peak may belong to. 


116 




SOLVENT FRONT SOLVENT FRONT 


ECD RESPONSE (TIME, MINUTES) 

0 2 4 6 8 10 12 14 16 18 20 



Figure 7 GC-ECD/PID combined (superimposed) chromatograms t or a mixture of P AHs and nitro P AHs w it h o nitrotolueneas 
internal standard. GC conditions used a 6—ft x 2.0-mm i.d., packed glass column of Permabond Methyl Silicone operated from 
40°C to 225°C at 15°C/min with temperature programming. Nitrogen carrier gas flow rate of 40 ml/min split ECD/PID. 


117 





































Table 5. RELATIVE RESPONSE FACTOR RATIOS ON ECD/PID FOR PAHs AND NITRO-PAHs® 


Compound Pair 

INDAN/5-NITROINDAN 

FLUORENE/2-NITROFLUORENE 

NAPHTHALENE/2-NITRO- 

NAPHTHALENE 

ANTHRACENE/9-NITRO- 

ANTHRACENE 

PYRENE/3-NITROPYRENE 


PID/PID 

4.6 x 10-1 
1.01 

2.3 x 10-' 
3.8 x 10-1 
1.00 


ECD/ECD 
3.1 x 10-5 

1.70 X 10-6 

2.70 x 10-3 
7.0 x 10-3 


ECD/PID-ECD/PID b 

6.80 X 10-5 

7.41 x 10-6 
4.88 x 10-3 

6.69 x 10-3 


a. ECD/PID relative response factor ratios were obtained on a 6—ft x 2.0-mm i.d. packed glass column of Permabond Methyl Sili¬ 
cone operated from 40°C to 225°C at 15°C/min with temperature programming and a nitrogen carrier gas flow rate of 15 
ml/min. Analyzed as mixtures of PAHs or nitro-PAHs with o-nitrotoluene present as internal standard. 

b. All calculations were done using peak heights and not peak areas. Relative response factor normalizations were done using o-ni¬ 
trotoluene as 1.00 on both ECD and P1D. 

c. It was not possible to obtain any measurable ECD response for fluorene at ug levels or above reaching the ECD. 


The above analyses and detector response fac¬ 
tors for these nitro aromatics, PAHs, and ni¬ 
tro-PAHs have been repeated on another Perma¬ 
bond PEG 20M type packing material, with GC 
separation conditions as indicated in Figure 8. 
This is a reconstructed GC-ECD/PID set of chro¬ 
matograms, wherein the GC-ECD and GC-P1D 
chromatograms were obtained separately via two 
injections of the same mixture of nitro derivatives, 
but utilizing different levels for each injection. 
The final two chromatograms have been superim¬ 
posed to yield Figure 8 for simplicity’s sake. 
Whereas it was not previously possible to baseline 
resolve 2,3- and 2,4-dinitrotoluene isomers, Fig¬ 
ure 5, with the Permabond PEG 20M packing ma¬ 
terial, this separation is readily achieved. Deter¬ 
minations of RRFs, normalized RRFs, and 
ECD/PID ratios of RRFs, as above, have now 
been made with the Permabond PEG 20M separa¬ 
tions, and these results are very similar to those al¬ 
ready presented, Table 2. 

Figure 9 is the GC-ECD chromatogram of a 
mixture of the three dinitrobenzene isomers to¬ 
gether with o-nitrotoluene, again using a Perma¬ 
bond PEG 20M packing material with the specific 
operating conditions indicated. These nitroaro- 
matics show no response on the PID at or below 
ug levels reaching the PID. 

The final chromatogram described here, Figure 
10, is the GC-PID chromatogram of five typical 
PAHs together with o-nitrotoluene as internal 
standard. These have been separated on a Perma¬ 
bond PEG 20M column, with the specific condi¬ 
tions as indicated in this Figure. The separation of 
naphthalene from the o-nitrotoluene is somewhat 
better on the Permabond PEG 20M than it was on 
the Permabond Methyl Silicone, as above, Figure 
6 . 


The almost unequivocal identification of a ni- 
troaromatic or nitro-PAH can be realized using 
the above ECD/PID ratios of normalized RRFs, 
together with single derivatization reaction de- 

ECD RESPONSE (time, min) 


0 2 4 6 8 10 12 14 16 

I-1_I_I_I_I_I_I_I 



Figure 8. GC-ECD/PID superimposed chromatograms of 
four isomeric dinitrotoluenes plus o-nitrotoluene analyzed on 
a 6-ft x 2.0-mm i.d. packed glass column of Permabond PEG 
20M at 10°C/min from 50°C to 180°C with nitrogen carrier 
gas flow rate of 35-40 ml/min. 


118 












































UJ 

c n 
2 
O 
CL 
CO 
UJ 
CC 


Q 

O 

UJ 


UJ 

M 

z 

UJ 

00 

o 

tr 


z 

o 

I 

Q. 


o 

V) 


10 

TIME 


~i-r 

8 6 

(MINUTES) 


1 I 

2 0 




Figure 9. GC-ECD chromatogram of the three dinitrobenzene 
isomers with o-nitrotoluene as internal standard, obtained on a 
6—ft x 2.0-mm i.d. packed glass column of Permabond PEG 
20M operated from 50°C to 180°C at 10°C/min with a carrier 
gas flow rate of 35-40 ml/min total. Amounts indicated are 
those reaching the detector. 


signed to convert the nitro group to an amino sub¬ 
stituent. A large number of useful and 
easy-to-apply chemical reductions have been de¬ 
scribed in the literature that will effect the conver¬ 
sion of a nitroaromatic into an aminoaromatic de¬ 
rivative. We have now applied this type of sin¬ 
gle-step derivatization to a large number of nitro- 
aromatics, as described above, and have then 
compared the RRFs for the starting nitro com¬ 
pound with the known/expected amine product. 



Figure 10. GC-P1D chromatogram of five typical PAHs plus 
o-nitrotoluene on a 6-ft x 2.0-mm i.d. packed glass column of 
Permabond PEG 20M operated at 15°C/min from 40°C to 
225 °C with a total carrier gas flow rate of 35-40 ml/min. 
Amounts indicated are those reaching the detector. 


At the same time, it has been possible to obtain ra¬ 
tios of ECD/PID RRFs, as already described for 
the nitro-PAHs and PAHs above, and these re¬ 
sults are indicated in Table 6. The farthest column 
on the right of Table 6 indicates the ratios of 
ECD/PID RRFs for each amine/nitro compound 


Table 6. NORMALIZED RELATIVE RESPONSE FACTORS VIA GC-ECD/PID FOR VARIOUS AROMATIC AMINE/ 
NITRO TYPE COMPOUNDS 2 


Compound Studied 1 * 

RRF- 

ECD 

RRF-PID 

RRF 

-ECD/PID 

Amine/Nitro Pair Ratio 1 ' 

p-TOLUIDINE 

8.64 x 

10-4 

0.585 


1.45 x 

10-3 

4.62 x 

10-4 

p-NITROTOLUENE 

1.46 


0.465 


3.14 


2,6-D1 AMI NOTOLUENE 

1.54 x 

10-3 

1.81 

10-2 

8.53 x 

10-4 

3.84 X 

10-6 

2,6-DlNlTROTOLUENE 

5.47 


2.46 x 

222.4 


2,4-DI AM I NOTOLUENE 

3.61 x 

10-3 

1.77 

10-2 

3.52 X 

10-3 

6.52 x 

10-6 

2,4-DINITROTOLUENE 

4.86 


9.00 x 

540.0 


2-AMINOFLUORENE 

9.48 x 

10-3 

1.79 


5.30 x 

10-3 

1.14 x 

10 -3 

2-N1TROFLUORENE 

3.48 


0.750 


4.64 


5-AM1NOINDAN 

1.66 x 

10-3 

3.26 


5.09 x 

10-4 

2.58 x 

10-4 

5-N1TROINDAN 

2.32 


1.18 


1.97 



a. Relative response factors were calculated using an internal standard, o-nitrotoluene as the base compound response on both 
ECD/PID, normalizing all such responses on a per ng or per ug basis, and then making these relative to the internal standard as 
1.00 on each detector. 

b. All compounds studied were obtained commercially, of the highest purity available. 

c. GC conditions used a Permabond Methyl Silicone column, 6-ft x 2.0-mm i.d., glass packed, with temperature programming in 
all cases. 


119 
















































pair. These are seen to be orders of magnitude dif¬ 
ferent, ranging from three to six orders in such 
overall ratio differences. Thus, the use of this type 
of derivatization for nitroaromatics, perhaps for 
nitro aliphatics, can provide yet further character¬ 
ization and speciation for unknown nitro com¬ 
pound present in complex sample matrices. 

With regard to the utilization of the above ana¬ 
lytical approaches for the identification and char¬ 
acterization of various explosives, we have studied 
four such compounds in dual ECD/PID detection 
in GC. Table 7 summarizes the RRFs via ECD and 
P1D for these four compounds, again using o-ni- 
trotoluene as the internal standard of reference. 


At the same time, we have determined the normal¬ 
ized ECD/PID ratios of RRFs, farthest column 
on the right in Table 7, which again provides 
quantitative data to identify an individual explo¬ 
sive that may be present in a complex sample ma¬ 
trix. In some cases, the explosive of interest, such 
as TNT or RDX, does not respond at all on the 
PID, but does, as expected, on the ECD. In other 
cases, tetryl and NG, there are satisfactory detec¬ 
tor responses on both ECD/PID, and one can 
then obtain a quantiative ratio of these RRFs, as 
indicated. Thus, at least these four explosives pro¬ 
vide widely different ECD/PID ratios of RRFs, 
data which could be used to differentiate one ex¬ 
plosive from another/others. 


Table 7. RELATIVE RESPONSE FACTORS AND ECD/PID RATIOS FOR EXPLOSIVES 8 


Compound Name 4 

RRF-ECD 

RRF-PID 

RRFs-ECD/PIDd 

o-NITROTOLUENE 

1.00 

1.00 

1.00 

TNT 

4.36 

_b 

— 

RDX 

1.60 

— 

— 

TETRYL 

3.00 

6.13 x 10-3 

48.94 

NG 

0.109 

6.71 X 10-3 

16.24 


a. GC conditions used a 6-ft x 2.0-mm i.d. glass packed column of Permabond Methyl Silicone operated from 50°C to 260°C at a 
temperature program of 15 °C/min with a nitrogen carrier gas flow rate of 22ml/min. 

b. These explosives did not respond on the PID at ug levels or below. 

c. Compound names: TNT = 2,4,6-trinitrotoluene; RDX = 1,3,5-trinitro-l,3,5-triazacyclohexane; TETRYL = 

2,4,6,N - tetranitro-N-methylaniline; NG = nitroglycerin. 

d. Calculations of normalized RRFs for these explosives were performed as described above for the other nitro derivatives, ni- 
tro-PAHs, etc. 


Clearly, the data presented above is only useful 
wherein the amounts of each nitroaromatic, PAH, 
and nitro-PAH reaching the detectors are within 
the linear portion of the calibration plot for such 
compounds on each detector. If amounts injected 
exceed such linear regions of the calibration plots, 
then the ECD/PID ratios so obtained would not 
be valid or reproducibly useful and/or applicable. 
Thus, for the analyst to use this approach he must 
first demonstrate that he is indeed working within 
the linear portion of his calibration plots for each 
compound of interest with each detector used. 
This has been demonstrated for all of the above 
compounds/data, wherein individual calibration 
plots have been obtained for at least one member 
of each class or group of nitro derivatives. The 
amounts of each compound reaching the two de¬ 
tectors in each and every case/study have now 
been shown to fall within the linear portion of the 
respective and applicable calibration plots. This is 
important to remember whenever ratios of detec¬ 
tor responses are to be used as a method of analyte 
identification and/or confirmation. 


ACKNOWLEDGEMENTS 

The authors wish to thank Barry Karger and 
Paul Vouros at Northeastern University for their 
continued interest in the application of GC-PID 
for organic nitro compound analyses. We also 
thank M. Hayes, D. Lewis, S.W. Jordan, and D. 
Bushee for their continued interest in this work. 

We very gratefully acknowledge the donation of 
an HNU Systems’ PID detector for use in all of 
these studies, as provided by the manufacturer of 
this equipment. Various packed GC columns, 
packing materials, PID lamps, and other acces¬ 
sories and materials/supplies were also donated to 
Northeastern University by HNU Systems, Inc. 
This work could not have been undertaken with¬ 
out such external industrial support, assistance, 
and collaboration. 

This work was financially supported, in part, by 
a contract from HNU Systems, Inc., to Northeast¬ 
ern University. Additional funding was provided, 
in part, by a National Institutes of Health (NIH) 
Biomedical Science Research Support Grant, No. 
RR07143, Department of Health and Human 


120 





Services, to Northeastern Universtiy. We grateful¬ 
ly acknowledge these sources of financial assist¬ 
ance. 

Most of the explosives standards used in these 
studies were obtained via the direct assistance of 
Dr. Terry Rudolph, FBI Academy, Forensic Re¬ 
search and Training Center, Quantico, Virginia. 
We acknowledge with appreciation the donation 
of these particular chemical standards. 

This is contribution number 166 from the Insti¬ 
tute of Chemical Analysis at Northeastern Univer¬ 
sity. 

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122 


DETERMINATION OF NITRO EXPLOSIVES BY GAS CHROMATOGRAPHY 
UTILIZING AN ON-COLUMN CAPILLARY INJECTOR 


Zelda Pen ton, Ph.D., Senior Chemist 
Varian Associates 
Walnut Creek Instrument Division 
Walnut Creek, CA 94598 


ABSTRACT. Nitroglycerin and other nitrated esters are important compounds 
because of ther use as explosives and as drugs in the treatment of cardiac disorders. 
The compounds have been determined by gas chromatography using conventional 
packed columns but the analysis can be quite difficult. Temperatures must be care¬ 
fully controlled and the column must be prepared and conditioned very carefully 
so that active sites on which the nitrated esters can decompose are eliminated. 
Capillary columns made of fused silica (pure synthetic SiOz without metal con¬ 
taminants) have been found to be of value when analyzing reactive compounds. 
When combined with a capillary on-column injector, many compounds that could 
not be analyzed by gas chromatography or could only be determined with great 
difficulty can now be measured. In this study, an election capture detector was 
used and nitroglycerin was determined down to sub-picogram levels. The sample 
was injected directly into the fused silica column under non-vaporizing conditions. 
There was no sign of tailing or decomposition. Linearity of response was examined 
over a concentration range of 10-3 and the correlation coefficient to a straight line 
was 0.997. In the discussion, the on-column injection technique will be described 
and contrasted with the older capillary injection techniques (split and splitless). 
Problems that one might encounter will be mentioned and results with other explo¬ 
sives such as nitramine and pentaerythritol tetranitrate will be given. 


Since the late 1970’s, improvements have oc¬ 
curred in the techniques of gas chromatography so 
that compounds of higher molecular weight and 
greater reactivity may be determined. The wide¬ 
spread use of fused silica capillary columns came 
first, followed by changes in the capillary inlet sys¬ 
tems. It is now possible to introduce a sample di¬ 
rectly into a fused silica column at temperatures 
well below the boiling point of all of the compo¬ 
nents. Thus gas chromatography has become a 
very practical technique for separating explosives. 

In this paper, the advantages of capillary gas 
chromatography with on-column injection will be 
described. The features of the Varian on-column 
injector will also be mentioned. In addition, the 
chromatographic conditions and results obtained 
in the separation of some nitro explosives will also 
be covered. The method is suitable lor trace analy¬ 
sis—the minimum detectable quantity ot nitro¬ 
glycerine is less than one picogram injected onto 
the column. 


Advantages of Capillary Columns and On- 
Column Injection 

In general, in almost any gas chromatographic 
analysis, capillary columns have many advantages 
over packed columns. Capillary columns offer far 
better resolution, resulting in relatively tall narrow 
peaks. The result is better separation of com¬ 
pounds of interest from interfering peaks, lower 
detection limits, and less errors in quantitation. 
Most capillary columns presently used are made of 
pure silicon dioxide without the metal contam¬ 
inants found in glass columns. The purity of the 
material of which the column is constructed re¬ 
sults in less tailing of polar compounds and less 
breakdown of reactive compounds. 

The technique of injecting the sample directly 
into a fused silica column under non-vaporizing 
conditions offers advantages over the traditional 
split-splitless inlet. These inlets are basically flash 
injectors—the sample is normally introduced into 


123 


a hot glass 1 2 liner where it evaporates quickly. 
Under these conditions, decomposition of labile 
compounds may occur as well as absorption of 
polar compounds on the hot glass liner or in the 
heated needle. For samples of wide boiling point 
range, discrimination also occurs in a split/split¬ 
less injector. The lowest boilers tend to evaporate 
prematurely and the highest boilers tend to remain 
in the needle so that the medium boilers are 
over-represented in the chromatogram. Cold 
on-column injection has been shown by Schom- 
berg et at. (1981) to result in less mass discrimina¬ 
tion than any other capillary injector technique. 

The Varian 1095 on-column injector (Figure 1) 
has several features that are worth mentioning. 
One of these features is an inlet that is sealed at all 
times. This prevents loss of very volatile com¬ 
pounds and makes flow controlled pneumatics 
possible. Thus, during temperature programming, 
the carrier gas flow remains constant and late elut¬ 
ing compounds come out somewhat sooner and 
with less peak broadening than would be possible 
in a pressure controlled system. The injector is 
also encased in a unit that allows cooling with 
liquid C0 2 or N 2 down to 0° Celsius and tempera¬ 
ture programming at a rate of 20° to 180° per 
minute up to 350°. This cooling and heating is en¬ 
tirely separate from the column oven. The sample 
is introduced with a 5 ^1 syringe that contains a re¬ 
placeable fused silica needle. The upper 
two-thirds of the needle is encased in a stainless 
steel sheath. The system is closed to the atmos¬ 
phere when the sheath enters the Teflon seal in the 
top portion of the injector. Table 1 shows results 
obtained with this injector for analysis of straight 
chain alkanes. 

Chromatographic Equipment and Conditions for 
Determination of Nitro Explosives 

The analyses were performed with a Varian 
6000 gas chromatograph equipped with a Model 
1095 on-column injector and electron capture de¬ 
tector. A Varian 401 chromatography data system 
was used for quantitation. 

The column was 0.32 mm x 12 meter fused silica 
coated with SE 30. A column was deliberately 
chosen with a film thickness of 0.5 micron : to 
minimize the possibility that exposed fused silica 
would contact the explosives and cause degrada¬ 
tion. It was necessary to use a new column that 

1 Some metal may also be present. 

2 Several film thicknesses are commercially available—the 
most common is 0.25 micron. 


rt : 7) SYRINGE 

© STOP 





Figure 1. Cross sectional diagram of the Varian on-column 
capillary injector. The fused silica column is inserted through 
the bottom and terminates in the wide portion of the glass 
alignment guide. The fused silica needle penetrates about 3 cm 
into the column. 

had never been heated above 250°. If a good 
column was used at the beginning and never over¬ 
heated, column life appeared reasonable—no 
degradation was evident after two months of use. 

An electron capture detector is necessary for 
trace analysis (< 1 nanogram injected). For larger 
quantities (1-200 nanograms), a flame ionization 
detector may be used. A nitrogen-specific detector 


124 





































TABLE 1. ACCURACY AND PRECISION FOR A WIDE BOILING RANGE MIXTURE OF NORMAL HYDROCARBONS 
WITH TEMPERATURE PROGRAMMED CAPILLARY ON-COLUMN INJECTION. 

Column: 15 M x 0.32 mm DB-5, 6 ml/rnin H 2 carrier gas, flow controlled. 

Averages of 5 consecutive runs. 

Oven: 70°C initial, 10°C/min to300°C. 

Injector: 70°C initial, 100°C/min to 300°C. 

Sample: Nominally 40 ng/jd each n-alkanes in isooctane. 0.5 ^1 injected. 



Factor 

•Vo R.S.D. 

Retention 

Time, Minutes 

R.S.D. 

Seconds 

N = 5 

% R.S.D. 

n-C 12 

0.996 

1.15 

3.249 

0.20 

0.103 

n-C 14 

0.999 

0.679 

5.592 

0.16 

0.047 

n-C 16 

0.979 

0.627 

7.846 

0.15 

0.031 

n-C| 8 

0.997 

0.211 

9.912 

0.15 

0.032 

n-C 22 

1.00 

— 

13.529 

0.16 

0.020 

n-C 26 

0.994 

0.314 

16.612 

0.24 

0.024 

n-C 30 

1.020 

0.187 

19.298 

0.25 

0.022 

n -C 3 6 

1.020 

0.714 

22.751 

0.31 

0.023 

n-C 40 

0.999 

0.512 

24.896 

0.42 

0.028 

n-C44 

1.010 

0.950 

28.500 

0.43 

0.025 


responded only to compounds in which there was 
a carbon to nitrogen bond and therefore was not 
suitable for nitroglycerine or pentaerythritol tetra- 
nitrate (Figure 2). 

GC conditions: 

Column oven: 40°C initial temperature, pro¬ 
grammed at 20°C/minute to 160°C, hold five 


minutes. 

On-column injector: 40° initial temperature, 
programmed at 60°C/minute to 160°C, hold 
nine minutes. 

Electron capture detector: 180°, range 10. 
Carrier gas: Helium, 4.5 ml/minute. 

Detector makeup gas: Nitrogen, 30 ml/minute. 


HC—ONO 

2 I 

HC—ONO„ 


HC— ONQ, 
2 2 


NITROGLYCERINE 



TRINITROTOLUENE 

TNT 


HC— ON0 2 


NOO—CH 2 —C—CH—ONO a 


HC—ONQ, 
2 2 


NO—N N- 


-NO„ 


GJ 



PENTAERYTHRITOL TETRANITRATE 

PETN 


CYCLOTHRIMETHYLENETRINITRAMINE 

RDX 


Figure 2. Structure of the explosive nitro compounds separated in this study. 


125 








TITLE: EXPLOSIVE STANDARDS 


CHANNEL NO: 2 

SAMPLE: 

STDS 

METHOD: EXPLOSIVES 



PEAK PEAK 

RESULT 

TIME 

TIME 

AREA 

SEP 


W1/2 

NO NAME 

NG/ML 

(MIN) 

OFFSET 

COUNTS 

CODE 


(SEC) 

1 NITROGLY 

101.6400 

5.351 

-0.009 

67126 

VV 

? 

0.80 

2 MDNB 

INT STD 

5.960R 

-0.010 

31572 

BV 


1.45 

5 TNT 

200.8060 

8.168 

-0.012 

98367 

BB 

? 

1.80 

7 PETN 

412.1790 

9.478 

-0.012 

77665 

VV 

? 

3.70 

8 RDX 

407.7500 

9.742 

-0.018 

127964 

VB 

? 

7.05 

TOTALS: 

1122.380 


-0.061 

402694 





Figure 3. Chromatogram and report of the explosive standards separated in this study. Chromatographic conditions are described 
in the text and in Table II. 


Results and Discussion 

Figure 3 shows the chromatogram obtained 
with the explosives mixture and the linearity 
curves are depicted in Figure 4. Table 2 sum¬ 
marizes the statistical parameters and minimum 
detectable quantity for each explosive. 

In conclusion, nitro explosives at the picogram 


level can be measured with reasonable precision 
and accuracy using an on-column capillary in¬ 
jector, fused silica column, and electron capture 
detection. This system would be suitable for quan¬ 
titating these compounds at very low levels such as 
in hand swabs. For larger quantities, the sample 
must be diluted or flame ionization detection 
might be employed. 


126 


























REFERENCE 


UJ 

</> 

Z 

o 

CL 

</> 

Ui 

QC 

Q 

U 

UJ 



NITROGLYCERINE 
TNT 

RDX 

PETN 


200 300 

PICOGRAMS 


500 


Schomburg, G., Husmann, H., and Rittmann, R. 
(1981). “Direct” (on-column) sampling into 
glass capillary columns—comparative investiga¬ 
tions on split, splitless and on-column sam¬ 
pling. J. Chrom. 204: 85-96. 


Figure 4. Linearity curves for several explosives. Each point is 
the average of three determinations. Precision data and corre¬ 
lation coefficient to a straight line are in Table II. 


TABLE 2. LINEARITY, PRECISION AND MINIMAL DETECTABLE QUANITY DATA FOR NITRO EXPLOSIVES WITH 
TEMPERATURE PROGRAMMED CAPILLARY ON-COLUMN INJECTION AND ELECTRON CAPTURE 
DETECTION. 

Column: 12 M x 0.32 mm fused silica coated with 0.5 micron SE 30. 

Carrier gas: Helium at 4.5 ml/minute. 

Oven: 40°C initial, 20°C/min to 160°C, hold 5 minutes. 

Injector: 40°C initial, 60°C/min to 160°C, hold 9 minutes. 

Detector: Electron capture at 180°C, range 10, 30 ml/min N 2 makeup gas. 

Sample: Dissolved in hexane at various levels, 1.4 microliters injected. 


Compound 

Correlation 
coefficient to 
a straight line 

25-500 picograms 

% RSD of response 
factor (relative 
to m-dinitroben- 
zene) n = 3 

Minimum detectable 
quanity 4 x noise 
level (noise was 
.019 millivolts 

Nitroglycerine 

.9982 

1.47 % (100 pg) 

.035 picogram 

Trinitrotoluene (TNT) 

.9992 

0.45% (200 pg) 

. 11 picogram 

Pentaerythritol 
tetranitrate (PETN) 

.9988 

3.53% (400 pg) 

.38 picogram 

Cyclotrimethylene- 
trinitramine (RDX) 

.9952 

2.85% (400 pg) 

.39 picogram 


127 





























































































































DIFFERENTIAL THERMAL ANALYSIS 
OF PYROTECHNIC COMPOSTIONS 


John A. Conkling 

Department of Chemistry 
Washington College 
Chestertown, MD 21620 


ABSTRACT. Differential thermal analysis (DTA) has proven to be a valuable 
tool for the identification and qualitative analysis of pyrotechnic and explosive 
mixtures as well as for the investigation of the chemical mechanism of pyrotechnic 
reactions. In DTA, processes that absorb heat from the surroundings, such as 
melting, boiling, and crystalline phase transitions, produce downward peaks, 
termed endotherms, in a plot of AT versus T (temperature difference between sam¬ 
ple and thermally-inert reference material). Processes that release heat, such as 
exothermic reactions, produce upward peaks (exotherms) in the plot. The resulting 
diagram, upon heating from room temperature to 500, 800, 1200° or higher, is 
termed a thermogram. The pattern for a particular pure material yields a thermal 
“fingerprint” that can be used for qualitative purposes and for purity determina¬ 
tions. The thermogram also yields information regarding the thermal stability of 
new materials and mixtures. The thermogram of a pyrotechnic or explosive mix¬ 
ture is a combination of the thermograms of the individual components, up to the 
ignition temperature of the material. At that point, a strong exothermic peak is ob¬ 
served corresponding to the occurrence of a self-propagating reaction. Typical 
thermograms of pyrotechnic and explosive materials will be presented, and some 
of the chemical implications regarding ignition behavior will be discussed. 


Differential thermal analysis (DTA) provides a 
rapid method for obtaining a thermal “finger¬ 
print” of an unknown material. The data ob¬ 
tained from such a study can be used for qualita¬ 
tive identification and for determining the possible 
explosive nature of an unknown solid material. 
Thermal analysis techniques can be particularly 
helpful when working with nonvolatile species, 
where other instrumental techniques such as gas 
chromatography/mass spectrometry (GCMS) are 
not applicable. 

In a thermal analysis study, one monitors the 
difference in temperature, AT, between the sample 
and a thermally-inert reference material as the 
sample and reference are identically heated from 
room temperature to a predetermined limit, typ¬ 
ically 500°C. Thermocouples placed in the sample 
and reference compartments measure any temper¬ 
ature difference that occurs during the heating 
process. A temperature difference will be observed 
if an exothermic or endothermic process occurs in 
the sample. Melting, boiling, and solid-solid 


phase transitions are processes that will momen¬ 
tarily cause the sample to be lower in temperature 
than the reference material, and a downward de¬ 
flection—known as an ENDOTHERM—is pro¬ 
duced in a plot of AT versus T (of the heating 
block). This plot is called a THERMOGRAM. 
Similarly, if an exothermic chemical reaction oc¬ 
curs in the sample, an upward deflection—called 
an EXOTHERM—will be produced. 

The pattern of exotherms and endotherms, 
versus temperature, is characteristic of a partic¬ 
ular sample and should be reproducible for a given 
material under a given set of experimental condi¬ 
tions. This fact makes DTA a valuable tool for the 
high-energy chemist, with many possible applica¬ 
tions including the following: 

1. Qualitative identification of unknown mate¬ 
rials 

2. Rapid indication of purity, by an examina¬ 
tion of the position and shape of the melting 
point endotherm 

3. Determination of reaction temperatures, in- 


129 


eluding the ignition temperatures of explo¬ 
sives and pyrotechnic materials. 

Note: Ignition temperatures are quite sensitive 
to the experimental conditions employed—heat¬ 
ing rate and sample size should be specified. 
Thermal analysis can therefore provide an 
abundance of information concerning the identity 
and reactivity of an unknown material, requiring a 
sample size of less than 10 mg, no pretreatment of 
the sample, and an analysis time of approximately 
10 minutes. Because of the small sample size, 
DTA is one of the safest techniques for laboratory 
personnel to use with unknown materials. 

The typical thermal pattern for unstable molec¬ 
ular solids is an endotherm for the melting point, 
followed by an exothermic decomposition at a 
temperature usually well below 500 °C. Most com¬ 
mon “high explosive” species—such as TNT, 
PETN, and RDX—display this pattern of thermal 
behavior (Figures 1 and 2). 

A type of explosive composition quite likely to 
be encountered in “home-made” and terrorist de¬ 
vices is a mixture of an oxidizer and a fuel, com¬ 


monly referred to as a pyrotechnic composition. 
Although usually less explosive in nature than the 
true “high explosives”, these compositions are 
capable of substantial destructive power when 
properly prepared and packaged. Pyrotechnic 
mixtures are normally prepared to produce visual 
and/or audible effects ( e.g ., fireworks), but they 
can be used for explosive purposes if the proper 
conditions are employed. 

These mixtures will vary enormously in be¬ 
havior, depending on the degree of mixing, the 
particle size of the ingredients, and the degree of 
confinement of the composition upon ignition. 
High confinement (e.g., powder loaded in a metal 
pipe) accelerates the burning process and can lead 
to an explosion for a mixture that will merely burn 
vigorously if ignited in the open. The ingredients 
commonly encountered in such mixtures include: 

1. Oxidizers—Oxygen-rich compounds such as 
potassium chlorate (KC10 3 ) and potassium 
nitrate (KN0 3 ). 

2. Fuels—Readily-oxidized materials that react 
with the oxidizer to produce heat and gas. 



Figure 1. Thermogram of pure TNT. An endotherm is observed for the melting point near 81 °C. A broad exotherm associated with 
decomposition can be seen at 300-330°C. 


130 












ENDO » - A T -► EXO 


Examples are Mg, Al, charcoal, and organic 
compounds such as sugar. 

3. Binder—Polymeric material added to blend 
the components together. The binder can 
also act as an extra fuel. 

In commercial pyrotechnic mixtures, other in¬ 
gredients are added to produce colored flames, 
smoke, burning rate control, and storage stability. 

These compositions can be quite exothermic 
upon ignition. Some representative enthalpy 
values are given in Table 1. As a comparison, TNT 
has a heat of explosion of 0.93 cal/gram. 


Table 1. TYPICAL HEATS OF REACTION FOR PYRO¬ 
TECHNIC MIXTURES 

Composition (% by weight) Heat of Reaction (Kcal/gram) 


KC 10 4 

66 

2.45 

Al 

34 


KCIO 4 

60 

2.24 

Mg 

40 


FE 2 0 3 

75 

0.96 

Al 

25 


KNO 3 

75 

0.66 

C 

15 


s 

10 


KC 103 

35 

0.38 

Lactose 

25 


Rhodamine 

(Dye) 

40 




Figure 2. Thermogram of pure PETN. A sharp melting point endotherm occurs near 140°, followed by exothermic decomposition 
above 200°C. 


131 












ENDO « --- A T .- » EXO 



Figure 3. Pure potassium nitrate. This thermogram shows a sharp endotherm for the rhombic-to-trigonal crystalline phase transi¬ 
tion near 130°C, and an endotherm for melting at 334°C. 


132 














SULFUR 

Rhombic - monoclinic transition 105°C 
Melting Point 113°C 
Liquid - liquid transition ^ 160°C 
Boiling Point ^ 440° C 



IOC 


MO 300 

T, °C (CHROMEL: ALUMEL)' 


40 O 


soo 


*M «»*T»UCT«H Mtkuti rot U*u COmCCTiO^ 


Figure 4. Sulfur. Endotherms for a rhombic-to-monoclinic crystalline phase transition and melting are seen at 105 °C and 119°C, 
respectively. An additional endotherm is observed near 170°. This peak corresponds to the fragmentation, in the liquid state, of 
8 -member sulfur rings into smaller units. Finally, an endotherm for vaporization is seen near 440°C. 


133 


SAMPLE:___RUN NO.; 















Figure 5. KNO 3 /S/AI Mixture. Endotherms for sulfur can be seen near 105 and 119°C, followed by the phase transition for potas¬ 
sium nitrate at 130°. As the melting point of K.NO 3 is approached (334°C), an exotherm is observed. A reaction has occurred be¬ 
tween the oxidizer and fuel, and ignition of the composition occurs. Apparently, once the solid lattice of the KNO 3 breaks down, 
intimate mixing of oxidizer and fuel can take place and a self-propagating reaction commences. 


134 











PURE POTASSIUM CHLORATE (kclo 3 ) 
Literature m.p. 356°C 


jl 


too 200 300 4 +oo soo 

T. °C (CHROMEL: ALUMEL) * *«. MTIVC'IO* MAMMAL • <30 KtU CO«Af(TlOM 

Figure 6 . Pure potassium chlorate (KCIO 3 ). No thermal events are observed prior to the melting point near 356°C. Exothermi 
composition of the compound occurs above the melting point, producing oxygen gas and potassium chloride (KC1). 



Figure 7. Sucrose (Cj 2 H 22 O] 1 ). A broad endotherm is observed commencing near 160°C. Sucrose decomposes as it melts over the 
temperature range 160-186°C. 


135 


SAMPLE:__RUN NO.: _ ? -RUN NO.:. 

























FIGURE 8. 

POTASSIUM CHLORATE (kclo 3 )/SUGAR 


66:33 BY WEIGHT 
Heating rate: 50°/minute 



o 

Q 

Z 

UJ 

_,_I-1——-1- 

too zoo 300 

T, °C (CHROMEL: ALUMEL)* 



_L_ 

H90 


_1 

500 


* 


SC* (HSTHwCTlO* *•»**»*». roil SCAlt CO»«£CTK>* 


Figure 8. KClOj/Sucrose. A thermal pattern quite similar to that of sucrose is obtained up to 175 °. At that point, a violent reaction 
occurred in the sample tube, expelling the thermocouple. Ignition was observed at the melting point of the fuel. The ignition temper¬ 
ature (180 °C) is well below the melting point of the oxidizer (356°C) for this mixture. 


REFERENCE 

Shidlovsky, A. A. Principles of Pyrotechnics 
(trans. from Russian), Report AD/A001859, 
Foreign Technology Division, Wright-Patter- 
son Air Force Base, 1974. Available from Na¬ 
tional Technical Information Service, Spring- 
field, VA. 

The thermogram for a pyrotechnic mixture will 
be a composite of the various components up to 
the occurrence of an exothermic reaction between 
the oxidizer and fuel, leading to ignition of the 
composition. Figures 3-8 illustrate the thermal 


patterns typical of oxidizers and oxidizer/fuel 
mixtures. Note in particular the Low ignition tem¬ 
perature of the potassium chlorate/sugar compo¬ 
sition. This behavior is typical of KCKh-contain- 
ing compositions, and indicates why such mixtures 
are hazardous to manufacture and prone to 
self-ignite. 

Differential thermal analysis can provide a 
rapid indication of the identity and potential haz¬ 
ard of many unknown compositions, and also can 
provide valuable data on ignition temperatures. 
DTA is an instrumental technique that should be a 
routine part of all laboratory investigations of 
high-energy materials. 


136 










IDENTIFICATION OF TWO RARE EXPLOSIVES 


Shmuel Zitrin, Shmuel Kraus and Baruch Glattstein 
Criminal Identification Division, 

Israel Police Headquarters, Jerusalem, Israel. 


ABSTRACT. Two unusual and rare explosives were identified in two separate 
cases of terrorist activity. The two explosives were identified as hexamethylene- 
diamine peroxide and triacetonetriperoxide. The identification was based upon in¬ 
terpretation of spectral characteristics of the compounds. These included mass 
spectrometry under electron impact (EIMS) and chemical ionization (CIMS) con¬ 
ditions, infrared (IR) spectrometry and nuclear magnetic resonance (NMR) spec¬ 
trometry. The explosives were first identified when no known spectra of them were 
available in our laboratory library. Their identity was later confirmed by com¬ 
parison with data from literature; the comparisons included melting points and IR 
spectra. The two explosives, which are organic peroxides, were described extensive¬ 
ly in older literature, but their current use as military explosives has not been re¬ 
ported. Although the explosive properties of the two compounds correspond to 
those of primary explosives, one of them, triacetonetriperoxide, was employed by 
terrorists as a main charge. Special significance should be given by law enforce¬ 
ment agencies to the simplicity of preparation of the two explosives, as well as to 
the ready availability of the starting materials needed for their synthesis. In the 
case of triacetonetriperoxide, the preparation was described in the testimony of an 
apprehended terrorist. An interesting point which could be relevant to the detec¬ 
tion of these explosives by X-rays is that contrary to common primary explosives 
(e.g ., lead azide or mercury fulminate), these peroxide explosives contain no metal¬ 
lic elements. Therefore their presence cannot be detected by standard airport se¬ 
curity procedures. 

Two explosives which had not been previously 
encountered in our laboratory were identified in 
cases related to terrorist activity. The two explo¬ 
sives, known as triacetonetriperoxide and hexa- 
methylenetriperoxidediamine (HMTD) are both 
organic peroxides which were first reported by 
German chemists in the late nineteenth century. 

The two explosives arrived at our laboratory as 
“completely unknown” samples and their identi¬ 
fication is described in this paper. In addition, 
new evidence for their structures is given. 

Triacetonetriperoxide (TATP, 1) was brought 
to our laboratory as a white powder found inside a 
pipe at the site of a terrorist attack in Hebron. It 
had been intended to be used as a main charge but 
only a part of it exploded. 

The powder, which had explosive properties, 
was found to be organic by its infra-red (IR) spec¬ 
trum (Figure 1). The IR spectrum lacked the char¬ 
acteristic absorption bands due to the streching vi- 


CH 3- \ / CH 3 

:c c< \ 


CH3 




CH3 


/ 

\ 


v 

/ 


CH^ ^CHg 


1 


brations of the nitro group (1). Our standard thin- 
layer chromatography (TLC) procedures (2), 
which have been designed to detect nitro-contain- 
ing explosives, failed to detect such explosives in 


137 


2 5 


MICROMETERS 


PERKIN ELMER 
4 5 


rth 


—! I- 


CHART NO. 1991042 
8 9 10 12 


14 16 20 25 


50 



the unknown powder. It was clear from the IR 
spectrum that the unknown explosive was not aro¬ 
matic. 

Mass spectra were recorded in both chemical io¬ 
nization (Cl) and electron ionization (El) modes. 
Most of the ion current in the El mass spectrum 
(Figure 2) was concentrated in the relatively unin¬ 
formative low mass region. The Cl mass spectrum 
(Figure 3), with isobutane as the reagent gas, was 
much more informative. The distinct ion at m/z 
223 could be attributed to the protonated mole¬ 
cule. A series of low abundant ions at m/z 101, 
117 and 133 differed by 16 m/z units, correspond¬ 
ing to the mass of an oxygen atom. This was the 
first clue that a peroxide could be involved. The 
similarity between parts of the El mass spectrum 
(Figure 2) and the El mass spectrum of acetone 
was noticed and the following preliminary litera¬ 
ture survey (3a) led us to the tentative identifica¬ 
tion of the unknown powder as TATP. It melted 
at 92°C, which was close to the melting point of 
TATP (3a). The IR spectrum (Figure 2) was reexa¬ 
mined and most of its absorption bands were ex¬ 
plained by the structure 1 of TATP. The band at 
872 cm -1 could be attributed to 0-0 streching vi¬ 
brations in peroxides (4). The IR spectrum 
matched the previously published spectrum of 
TATP (5). 


The 'H-nuclear magnetic resonance (NMR) 
spectrum showed that all the protons absorbed as 
a singlet, at a chemical shift (d) ~ 1.47 p.p.m. (in 
CDClj). According to a previous NMR study (6), 
TATP has chiral molecules and could potentially 
be resolved into two enantiomers. 

TATP or 3,3,6,6,9,9-hexamethyl-l,2,4,5,7,8- 
hexoxonane was first prepared by Wolffenstein in 
1895 (7) by a reaction between acetone and 30% 
H;O; in the presence of an acid. A white crystal¬ 
line product was obtained; it exploded violently by 
friction. 

Hexamethylenetriperoxidediamine (HMTD, 2) 
was brought to our laboratory as a white powder 
from a detonator. The detonator, which was made 
of plastic instead of metal, was found on a woman 
crossing a bridge over the Jordan river. 


O —O 

N -CH 9 —0 — 0 

\ 

CH 2 —0—0 


■CHo 

\ 

CHg - N 

CH2^ 


Normal TLC procedures (2) failed to detect ni- 
tro-containing explosives in the white powder. 
The IR spectrum (Figure 4) had no absorption 


138 


SAMPLE_REF. NO 





















































































































































































































































































RELATIVE ABUNDANCE ( V. I 


bands related to nitro groups. It also showed the 
absence of aromatic compounds. 

El (Figure 5) and Cl (Figure 6) mass spectra led 
to the identification of the powder. A molecular 
weight of 208 is clearly indicated by the molecular 
ion in the El mass spectrum (Figure 5) and by the 
[M + H] + and [M + C 4 H 9 ] + ions in the Cl-isobu- 
tane mass spectrum (Figure 6). 

The loss of 32 m/z units from the molecular ion 
in the El mass spectrum could indicate a loss of 0 2 
(although loss of 32 m/z units is usually associated 


in mass spectrometry with methanol elimination). 
An examination of the IR spectrum (Figure 4) in¬ 
dicated the possible presence of an 0-0 stretch¬ 
ing vibration at 875 cm -1 (4). Once the possibility 
of a peroxide was considered, a literature survey 
(3b, 8) led to the identification of the powder as 
HMTD. The powder melted at 145°C, which was 
similar to previously reported values (3b, 8). 


100 


80 


60 


40 


20 


TATP 

El 


20 40 60 80 too 120 WO 160 180 200 

m/z 


Figure 2. The El mass spectrum of TATP (7). 



1 1 L*- -V U I - f ,-- -r- r* - 

40 60 80 KX> 120 140 160 180 200 220 240 


m/z 

Figure 3. The Cl-isobutane mass spectrum of TATP (7). 


1 i I i i n ~~ I I 

PERKIN ELMER *' CHART NO. 199-1042 

2.5 3 MICROMETERS 4 5 6 7 8 9 10 12 14 16 20 25 50 



Figure 4. The IR spectrum of HMTD (2). 


139 











































































































































































































































































































































RELATIVE ABUNDANCE C/.l 


lOO 


80 


60 


40 


20 


42 


HMTD 

El 


LI l 


[M^208 


176 


I 


UL 


40 60 80 100 120 140 160 180 200 220 

m/z 


Ui 

o 

z 

< 

o 

z 

3 

CD 

< 


> 

5 


100 

80 

60 

40 

20 


HMTD 

Cl-isobutane 

(min. relative intensity 57. ) 


74 104 


[M'H] 


2 65 


60 80 100 110 140 160 180 200 220 240 260 280 

m/z 


Figure 5. The El mass spectrum of HMTD (2). 


Figure 6. The Cl-isobutane mass spectrum of HMTD (2). 


When the powder reached its melting point, the 
capillary tube containing it exploded violently. 
The fragmentation patterns in the El (Figure 5) 
and Cl (Figure 6) mass spectra could be ration¬ 
alized by the structure of HMTD. The IR spec¬ 
trum (Figure 4) matched a previously reported one 
(9). 

HMTD was first prepared by Legler in 1881 (10) 
by oxidizing formaldehyde with H 2 0 2 and reacting 
the product with ammonia. The structure^ was 

proposed by Baeyer and Villiger in 1900 (11). An 
alternative structure ^ was proposed by Grisewald 

and Siegens in 1921 (12). 


O-CHo .CHg-p 

'^n-ch 2 -o-o-ch 2 -nC^ 

O-CH2 ^CK^-O 


Both formulae, 2 and 3, were mentioned by Ur- 
banski (8). The chemical abstract nomenclature is 
based on structure 2: 3,4,8,9,12,13-hexaoxa- 
l,6-diazabicyclo[4.4.4] tetradecane, probably fol¬ 
lowing the IR study of Ferroni et al. (9). The mass 
spectra (Figures 5 and 6) could not differentiate 
unequivocally between the two structures. The 
highly abundant ion at m/z 88 in the El mass spec¬ 
trum (Figure 5) may result from the molecular ion 
of 3 by a simple a cleavage. It may also result from 

the molecular ion of 2 through an extensive rear¬ 


rangement. ‘H-NMR of HMTD points to struc¬ 
ture^: only one type of methylene protons ap¬ 
pears at 6 ~ 4.7, p.p.m. showing an expected AB 
pattern. As HMTD is insoluble in water or most 
organic solvents, the NMR spectrum was run in 
dimethyl sulfoxide-d* (DMSO-<T). I3 C-NMR (in 
DMSO-d 6 ) also supports structure^: the carbon 

atoms resonate as a singlet, at a chemical shift 
89.3 p.p.m. 


REFERENCES 

1. J. Yinon and S. Zitrin. “The Analysis of Ex¬ 
plosives”, Pergamon Press, Oxford, pp 
156-158 (1981). 

2. M. A. Kaplan and S. Zitrin. J. Assoc. Off. 
Anal. Chem., 60, 619(1977). 

3. B. T. Fedoroff and O. E. Sheffield. “Encyclo¬ 
pedia of Explosives and Related Items”, Pica- 
tinny Arsenal, Dover, N.J. a) Vol. 7, pp 
A42-A45 (1960). b) Vol. 7, pp H83-H84 (1975). 

4. L. J. Bellamy. “The Infrared Spectra of Com¬ 
plex Molecules”, Methuen & Co., London, p. 
120(1962). 

5. N. A. Milas and N. Golubovic. J. Am. Chem. 
Soc., 81, 6461 (1959). 

6. F. A. L. Anet and I. Yavari. Tetrahedron Lett. 
3787 (1976). 

7. R. Wolffenstein. Ber., 28, 2265 (1895). 

8. T. Urbanski. “Chemistry and Technology of 
Explosives”, The Macmillan Co., N.Y. Vol. 3, 
p. 225 (1964). 


140 



















9. E. Ferroni, F. Ciampelli and G. Serboli. 4th 

Proc. Intern. Meet. Mol. Spectroscopy, Bolo- 
nia, 2, 762 (1959) (published 1962). 

10. L. Legler. Ber.,/4, 602 (1881). 


11. A. Baeyer and V. Villiger. Ber., 33, 2479 
(1900). 

12. C. von Girsewald and H. Siegens. Ber., 54, 
490(1921). 


141 






































IDENTIFICATION AND QUANTITATION OF AN UNKNOWN EXPLOSIVE 

Tung-ho Chen 
Energetic Materials Division 
Large Caliber Weapon Systems Laboratory 
U.S. Army Armament Research and Development Command 
Dover, New Jersey 07801 

ABSTRACT The methodologies employed in the identification, structural deter¬ 
mination, and quantitation of the constituents of an unknown explosive mixture 
will be described. The techniques used include chemical tests, elementary analysis, 
thin-layer chromatography (TLC), infrared absorption spectrophotometry (IR), 
ultraviolet-visible absorption spectrophotometry (UV-VIS), nuclear magnetic 
resonance (MMR), gas chromatography/mass spectrometry (GS/MS), positive 
and negative ion chemical ionization mass spectrometry (PINICIMS), and high 
resolution electron impact mass spectrometry (HREIMS). The structural deter¬ 
minations were based primarily on the HREIMS data along with chemical stability 
considerations, the molecular weight and the structural data derived from 
PINICIMS, NMR, and IR. The positive identification of the unknown was made 
by synthesizing the compound and comparing its characteristics with those of the 
unknown in question by various instrumental techniques. Both NMR and HPLC 
were used in the composition analysis. 

INTRODUCTION 

Recently, this Laboratory was involved in the 
difficult task of analyzing an unknown liquid ex¬ 
plosive mixture which had never been encoun¬ 
tered. In this paper, the methodologies employed 
for the identification, structural determination, 
and quantitation of the constituents in the mix¬ 
ture, together with part of the experimental re¬ 
sults, will be described. 

INITIAL RESULTS 

The unknown explosive was a clear, pale yel¬ 
low, viscous liquid with a pungent odor. Various 
techniques were initially used to identify the un¬ 
known. These included chemical tests, mi¬ 
croscopic observations, elemental analysis, 
thin-layer chromatography (TLC), high perfor¬ 
mance liquid chromatography (HPLC), infrared 
absorption spectrophotometry (IR), ultravio¬ 
let-visible absorption spectrophotometry (UV- 
VIS), proton nuclear magnetic resonance (NMR), 
gas chromatography/electron impact mass spec¬ 
trometry (GC/EIMS), and direct-inlet probe mass 
spectrometry (DIPMS). 

Figures 1,2, and 3 show, respectively, the repre¬ 


sentative mass spectra for the low-, medium-, and 
high-boiling fractions of the sample with m/e of 
43, 137, and 185 as the respective base peaks. 
These three distinctly different mass spectra were 
obtained during repetitive scanning of samples by 
DIPMS. During this experiment, which used es¬ 
sentially a crude MS/MS technique, the sample 
was heated slowly from ambient temperature to 
about 300°C and the spectrum scan continued un¬ 
til no useful spectrum could be obtained. These 


LE 27 0 MIN 28 SEC 23 OCT 73 160 E 

HIGH MASS 207 LOW MASS 26 MASS INTENSITY 



Figure 1. Mass Spectrum of Low-Boiling Fraction of Un¬ 
known Explosive 

(Scan No. 27; Scan Time 28 Sec) 


143 










IE 65 


1 MIN 26 SEC 23 OCT 73 


407 


85 N 

HIGH MASS 270 LOW MASS 26 MASS INTENSITY 



Figure 2. Mass Spectrum of Middle-Boiling Fraction of Un¬ 
known Explosive 

(Scan No. 85; Scan Time 86 Sec) 

LE 103 1 MIN 44 SEC 23 OCT 73 5 Y 

HIGH MASS 429 LOW MASS 26 MASS INTENSITY 



Figure 3. Mass Spectrum of High-Boiling Fraction of Un¬ 
known Explosive 

(Scan No. 103; Scan Time 104 Sec) 

spectra revealed the following; (1) the unknown 
explosive was a multicomponent mixture; (2) it 
was nonaromatic; (3) it contained at least one 
chlorine atom (m/e 137, 139, and 183, 185 with in¬ 
tensity ratios of 3 to 1) NO; group(s) (m/e 46 and 
30), and possibly, a CH 3 CO group (m/e 43); and 
(4) the molecular weights of the constituents were 
at least 200. 

Figure 4 shows a reconstructed ion chromato¬ 
gram (RIC) obtained in the GC/MS experiment. 

Peaks 86 and 762 are solvent and column con¬ 
tamination, respectively. The peak shapes near 
Scan No. 529 suggested the possible presence of 
labile component(s) in the unknown. 

Figure 5 depicts high performance liquid 
chromatograms of the unknown. 

The results obtained by DIPMS, GC/MS, and 
HPLC indicated the presence of more than three 
compounds in the sample. Thin layer chromato¬ 
graphy was also employed in an attempt to sepa¬ 
rate various constituents of the unknown. How- 



scan time 3:30 7:00 10:30 14:00 17:30 21:00 24:30 

Figure 4. Reconstructed Ion Chromatogram of Unknown Ex¬ 
plosive 



Figure 5. High Performance Liquid Chromatograms of Un¬ 
known Explosive 



Figure 6. Infrared Spectrum of Unknown Explosive 


ever, even with the use of high performance TLC 
plates, only partial separation was achieved. This 
was demonstrated in the analysis of the extracts 
obtained from various zones of the developed 
plate by DIPMS in the “crude MS/MS” mode de¬ 
scribed earlier. 

Figure 6 shows the infrared spectrum of a neat 


144 







































































AMPLITUDE 


sample of the unknown. The absorption frequen¬ 
cies and the possible group assignments are sum¬ 
marized in Table 1. It should be noted that the IR 
group assignments were difficult due to the strong 
influence of other structural features of the com¬ 
pounds on the absorption frequencies. 

Table 1. INFRARED ABSORPTION FREQUENCIES OF 
UNKNOWN EXPLOSIVE AND POSSIBLE 
GROUP ASSIGNMENTS 


Legend: S = strong; M = medium; and W = weak 

Possible Group 


Absorption Frequencies, cm-' 

3000 (W), 2960 (W), 2920 (W) 

1777 (S), 1742(S) 

1600 (S), 1440 (M), 1390 (W), 1340(W) 
1310 (S), 1210 (S), 1130 (M), 1080 (M) 
1040 (M), 1000 (W), 920 (W), 855 (M) 
820 (M), 800 (M), 780 (M) 


Assignments 

Alkane 

Ester 

r-no 2 


In Figure 7, the 60 MHz proton nuclear magne¬ 
tic resonance spectrum is shown. The chemical 
shifts and the possible group assignments are sum¬ 
marized in Table 2. The observed chemical shifts 
clearly ruled out the presence of nitroaromatic 
compounds as well as nitramines. Furthermore, 
the lack of hydrogen coupling indicated that the 
compounds in the unknown mixture exhibited 
high degrees of symmetry. These observations 
played an important role in the ultimate structural 
determinations. The unknown sample exhibited 
strong absorption in the 200 to 240 nm range, the 
absorbance being the strongest at 200 nm, which is 
the low cut-off wavelength of the instrument used. 
The maximum absorption wavelength was, there¬ 
fore, likely to be located near 200 nm or in the va¬ 
cuum ultraviolet region. The observed absorption 
range coincided with those of polynitro com¬ 
pounds such as nitramines. Aside from this useful 



PPM (61 

Figure 7. 60 MHz Proton Nuclear Magnetic Resonance Spec¬ 
trum of Unknown Explosive 


information, however, UV absorption spectra 
provided little additional insight into the identities 
of the unknowns. 

Table 2. CHEMICAL SHIFTS OF 60 MHz PROTON NU¬ 
CLEAR MAGNETIC RESONANCE OF UN¬ 
KNOWN EXPLOSIVES AND POSSIBLE GROUP 
ASSIGNMENTS 

Legend: S 

Chemical Shift (d, ppm) 

5.35 (S), 5.2 (S) 

4.9 (S), 4.6 (S) 

3.75 (S) 

3.35 (T), 2.7 (T) 

2.1 (S) 

Various chemical tests were also carried out, the 
most significant observation being the pro¬ 
nounced effect of treatment with aqueous, alka¬ 
line solution on the IR spectrum of the sample. 
The absorptions near 1700 cm 1 were greatly re¬ 
duced, indicating the presence of ester linkages, 
which apparently hydrolyzed under this treat¬ 
ment. 

Only cursory examinations of the unknown 
were made by fast atom bombardment mass spec¬ 
trometry (FABMS) and Fourier transform mass 
spectrometry (FTMS). These experiments were 
performed during demonstrations of these instru¬ 
ments which had just been introduced into the 
commercial market. Due to the very limited nature 
of the experiments, no useful information could 
be extracted from the data obtained. 

Attempts were then made to match the existing 
spectroscopic and chromatographic data files, in 
particular, the EIMS files of known explosives 
with the experimental data. However, these ef¬ 
forts were not successful. Peak No. 762, the col¬ 
umn contaminant, and Peak No. 1014 were identi¬ 
fied to be methyl stearate and di (2-ethylhexyl) se- 
bacate, a plasticizer, respectively. 

At this point, all experimental evidence indicat¬ 
ed that the explosive constituents of the unknown 
consisted of nitroaliphatic compounds which were 
not in common use. 

STRUCTURAL DETERMINATION 

Although considerable structural information 
was obtained in the preliminary studies, especially 
by GC/EIMS, the lack of molecular weight infor¬ 
mation hampered the structural elucidation. This 
information is especially important for the type of 
compounds under investigation which produce 


= singlet; T = triplet 

Possible Group Assignment 

-0-CH 3 

O - 

II 

-C-CH, 


145 













primarily small fragment ions under the condi¬ 
tions of EIMS. Additional experiments were, 
therefore, conducted to obtain this necessary in¬ 
formation as well as other data crucial to the 
structural determinations. The methodologies em¬ 
ployed will be described in this section. Of the 
methodologies used, DIP high resolution (HR) 
EIMS ranked as the most powerful since this tech¬ 
nique provided unequivocal data regarding the ex¬ 
act elemental compositions of fragment ions as 
well as the structural data essential for the struc¬ 
tural elucidation of the unknown compounds. 
Next to HREIMS in usefulness were DIP positive 
ion chemical ionization (PIC1) MS and negative 
ion chemical ionization (NIC!) MS from which 
key molecular weight information was deduced. 
Closely ranking behind these two techniques in 
usefulness were GC/EIMS and GC/PICIMS 
which permitted rapid separation and character¬ 
ization of nonlabile constituents of the unknown 
explosive. These techniques were extremely sensi¬ 
tive and required only minute quantities of sam¬ 
ples for analyses. Although not as sophisticated 
and powerful as various versions of GC/MS, 
DIPEIMS operated in the “crude MS/MS” mode 
was capable of generating useful structural data. 
Aside from these powerful MS techniques, NMR 
and IR, the former, in particular, provided sup¬ 
plementary structural data which facilitated the 
identification of the unknowns. The lower sensi¬ 
tivities of NMR and IR, however, limited their 
usefulness. Preparative HPLC played an impor¬ 
tant role in providing required quantities of the 
constituents of the unknown explosive for various 
structural studies. The advantage of HPLC laid in 
its ability to isolate nonvolatile and labile species 
without causing degradation. 

Isolation of Pure Components 

Preparative HPLC was used to isolate sufficient 
quantities of pure explosive components needed 
for structural determinations and confirmations 
by MS, NMR, IR, UV, and HPLC. This was ac¬ 
complished by multiple injections of concentrated 
explosive sample solutions into the analytical 
HPLC column under normal phase operations 
and multiple successive collections of Peaks No. 1 
to No. 3 (see Figure 5) fractions. The collected 
fractions were then freeze-dried to isolate the pure 
components. Freeze-drying was employed to in¬ 
sure the recovery of volatile and labile compo¬ 
nents. The procedure used permitted the collection 
of pure materials directly into 1 mL graduated 


concentration tubes. Peak No. 1 was later tound 
to be a mixture of two compounds. However, no 
further separation was required to determine their 
structures. 

Determination of Empirical Formulas of frag¬ 
ment Ions 

Accurate mass assignments to ± 6 millimass 
units of fragment ions were carried out by 
DIPHREIMS using both the neat mixture and the 
pure isolated components. This enabled the deter¬ 
minations of empirical formulas for fragment ions 
which could be assigned to various fragmentation 
patterns obtained by GC/EIMS even in the case ot 
a mixture. 

Determination of the Molecular Weights of Ex¬ 
plosive Constituents 

The pseudo-molecular ions of explosive constit¬ 
uents were obtained by DIPPINICIMS using the 
separated components, with water as the reagent 
gas and also by GC/PICIMS with methane as the 
reagent gas. From the structural information ob¬ 
tained by HREIMS and other techniques, the mo¬ 
lecular weights of the explosive constituents were 
deduced from the pseudo-molecular ions. It 
should be pointed out that the correct molecular 
weight assignments were often complicated by the 
lack of data for interpreting the unknown CIMS 
spectra. Moreover, both PICIMS and NICIMS 
spectra were found to be essential in the molecular 
weight determination. 

Structural Elucidations 

This represented the most difficult and interest¬ 
ing part of this work. The general approach was to 
arrive at the most probable structure by taking in¬ 
to consideration primarily the HREIMS data and 
the molecular weight, together with other struc¬ 
tural data derived from PINICIMS, NMR, and 
IR. In addition, the chemical stability of the pro¬ 
posed structure was carefully considered. This in¬ 
cluded a literature search on the proposed struc¬ 
ture and similar types of compounds. The main 
problem encountered in this work was to deter¬ 
mine the structural features missing in both EIMS 
and CIMS spectra. For example, in Figure 8, very 
little structural information was available between 
m/e of 131, the largest fragment ion observed in 
EIMS, and 224, the pseudo-molecular ion of Peak 
No. 288 obtained by PICIMS. In two other cases, 
the information gaps amounted to approximately 
50% of the molecular structures. This problem 
arose of course, from the fact that CIMS pri- 


146 



Figure 8. Mass Spectra of Peak No. 288 


marily provided pseudo-molecular ion informa¬ 
tion whereas EIMS of explosive compounds in 
question gave rise to small fragment ions. Nuclear 
magnetic resonance and a knowledge of chemical 
stability played important roles in filling these 
gaps. 

Structural Confirmation 

This was accomplished by synthesizing the com¬ 
pound and comparing its spectroscopic and chro¬ 
matographic characteristics with those of the un¬ 
known in question by EIMS, NMR, 1R, UV, and 
HPLC. 


COMPOSITION ANALYSIS 

The composition of the unknown explosive was 
determined by HPLC and NMR. In the case of 
HPLC, synthetic external standards were em¬ 
ployed. One component had to be determined by 
difference due to the lack of a pure standard. 
Using NMR, the integrated areas were used in the 
composition analysis and no standards were 
needed. Both methods, which are independent, 
gave essentially identical results. 

SUMMARY 

The methodologies employed in the identifica¬ 
tion, structural determination, and quantitation 
of the constituents of an unknown explosive mix¬ 
ture have been described. The techniques used in¬ 
cluded chemical tests, elemental analysis, TLC, 
IR, UV-VIS, NMR, GC/MS, P1NICIMS, and 
HREIMS. 

The structural determinations were based pri¬ 
marily on the HREIMS data along with chemical 
stability considerations, the molecular weight, and 
the structural data derived from PINICIMS, 
NMR, and IR. The positive identification of the 
unknown was achieved by synthesizing the sus¬ 
pected compounds and comparing their character¬ 
istics with those of the unknowns in question by 
various instrumental techniques. Both NMR and 
HPLC were used in the composition analysis. 


147 




































































* 












ANALYSIS OF AN UNUSUAL EXPLOSIVE: 

METHODS USED AND CONCLUSIONS DRAWN FROM TWO CASES 

Reutter, Dennis J.; Bender, Edward C.; and Rudolph, Terry L., 

Federal Bureau of Investigation 


ABSTRACT. Samples of explosive material are often submitted to the FBI La¬ 
boratory for identification. In most cases, the sample is quickly identified by Gas 
Chromatography/Mass Spectrometry analysis and, if a sufficient quantity of pure 
substance is available, by Infrared Spectroscopy. The resulting spectra are com¬ 
pared with library spectra or spectra obtained from known samples in the labora¬ 
tory. When no matching spectra can be found among these resources, the examiner 
must deduce the molecular structure of the material by using fundamental chemi¬ 
cal knowledge and by employing whatever appropriate spectroscopic techniques 
are necessary. The choice of those techniques will depend both on the quantity of 
material available and on the complexity of the structure. Two recent cases will be 
discussed with emphasis on the methodologies used by the examiners. 


One of the many tasks of the FBI Laboratory is 
the identification of explosive materials which are 
linked to criminal activity or threats to national se¬ 
curity. Most of the cases are routine; the sample 
can be analyzed by gas chromatography/mass 
spectroscopy or infrared spectroscopy and with 
the aid of a data system, correctly identified with¬ 
in an hour. Occasionally, a sample is encountered 
where the components have not been seen by any 
of the personnel in the Laboratory, and the spec¬ 
tra are not recorded in any of the data bases. Such 
cases force the examiner to use several different 
types of analytical equipment and piece together 
the information given by each instrument. 

There is no set procedure which will be success¬ 
ful in every case. The tests which are most appro¬ 
priate for a particular sample depend on the sam¬ 
ples quantity and purity as well as the chemical na¬ 
ture of the explosive material itself. The examiner 
will be constrained by the availability of equip¬ 
ment and the expertise of the personnel in the lab¬ 
oratory. 

This paper is about two different explosives 
which were found in two different cases. These ex¬ 
plosives were unusual only in that they had not 
been seen before by anyone in the FBI and were 
not present in any of the collections of spectro¬ 
scopic data available within the laboratory. The 
lessons learned by the examiners in these cases 
have led to some changes in the way future cases 
involving similar materials will be handled. 


The first case centered on a sample of white 
powder which was brought to a FBI field office by 
an informant who claimed it was new type of high 
explosive which illegally entered this country. A 
subsequent investigation established that the pow¬ 
der had originated from a professional chemist 
who lives in western Europe and had several busi¬ 
ness dealings with countries in Eastern Europe and 
the Middle East. 

Approximately 2 grams of the powder was sent 
to the FBI Laboratory for analysis. Initially it was 
subjected to the tests normally performed on rela¬ 
tively large samples of explosives. Milligram quan¬ 
tities of the powder were found to instantaneously 
combust when brought within a centimeter of an 
open flame. The powder was relatively insensitive 
to shock, and was only slightly soluble in acetone, 
water, toluene and heptane. Dimethyl sulfoxide 
proved to be a moderately good solvent for the 
powder. The sample melted over a range of 149 to 
150 degrees Celsius indicating a single component 
of fairly high purity. 

A saturated methylene chloride extract was in¬ 
jected without dilution into a HPLC system which 
was set up to screen for all the nitrate esters, nitro- 
aromatics and nitramines common to commercial 
and military explosives. The mobile phase was 
60% iso-octane and 40% methylene chloride and 
the column was 25 cm x 4.6 mm packed with 5 
mm spherical silica. A UV abroption detector set 
at 254 nm preceeded a Thermal Energy Analyzer 


149 


(TEA) which was operated with the pyrolysis 
chamber at 550 degrees Celsius. In this mode the 
TEA was specific for compounds with -N-O, 
0-NO 2 functional groups. The chromatographic 
run produced no response on the UV absorbance 
detector and two very small peaks on the TEA 
which were consistant with, a few nanograms at 
most of nitrated material. The two peaks on the 
TEA trace was interpreted to be impurities in the 
sample. 

Gas chromatography—mass spectroscopy (GC/ 
MS) of the powder proved to be very difficult. No 
peaks were observed following the solvent peak on 
the RIC (50-500 M/E) when a methylene chloride 
extract was injected through a Grob type injector 
onto a fused silica capillary column coated with 
cross-linked methyl silicone. A very poorly 
shaped peak (see Figure 1) did appear on the RIC 
when the extract was injected with a cold, 
on-column injector onto a similar column which 
was directly coupled to the mass spectrometer 
source. Several runs were made varing the GC and 
mass spectrometer source conditions to optomize 
the analysis. The compound would not chromato¬ 
graph if the oven temperature reached 150 degrees 
Celsius before elution into the ion source. The 
electron impact mass spectrum was very depen¬ 
dent on the source temperature and somewhat de¬ 
pendent on the GC interface temperature. Figure 2 
represents one of the El spectrum obtained. The 
M/E = 208 was interpreted to be M + and M/E 
= 176 was apparently loss of 0 2 . The loss of 
methanol was not ruled out but was thought un¬ 
likely because no evidence of loss of -CFT or -OF1 
was apparent. The absence of M/E 46 or 30 con¬ 
firmed the conclusion drawn from the earlier 
HPLC run that the explosive was not a nitrate est¬ 
er. The ratio of the 209/208 was .06 indicating 6 
carbons in the 208 ion. 



Figure 1. Total ion chromatograph of unknown explosive 



Figure 2. Electron impact (70eV) mass spectra of unknown 
explosive powder 

Chemical ionization GC/MS using .22 torr (in¬ 
dicated) methane and a source temperature of 250 
degrees Celsius resulted in the mass spectrum 
shown in figure 3. The ion at M/E = 209 was in¬ 
terpreted as (M+l)+, and the ion at M/E 191 
was thought to be (M + H - H ; 0) + . No other ions 
were assigned in the spectrum, nor were they cor¬ 
related with the El mass spectrum. 

A KBr pellet was made from the powder after 
drying over a dessicant overnight and an infrared 
spectrum was obtained as shown in Figure 4. The 
bands at 2970 and 2930cm 1 were consistent with 
C-H stretch. The broad peak at 1680cm“' was 
thought to be the key to successfully interpreting 
the spectra, however, no assignment could be 
made which was consistant with the rest of the 
spectra. It was later shown that this band was due 
to an impurity. With the exception of those bands 
which could be assigned to a C-H bond, no other 
absorption bands were assigned. 

X-ray diffraction of the powder produced the 
pattern shown in Figure 5. That pattern did not 
match any published patterns on the references 


209 



Figure 3. Methane chemical ionization spectrum of unknown 
explosive powder 


150 









































Figure 4. Infrared spectrum of unknown explosive powder 
(KBr Pellet) 



Figure 5. X-ray powder diffractogram 


available within the laboratory, but was quite 
helpful because it indicated a crystal structure of 
high symmetry. 

At this point there was little else that could be 
accomplished with the equipment available within 
the FBI Laboratory. The available information 
was not sufficient for the scientists on the staff to 
determine the identity of the explosive. 

It was decided to go outside the FBI and request 
the assistance of FDA-Bureau of Foods. They 
possessed a high resolution mass spectrometer, 
and a 1 H and a l3 C NMR which would prove essen¬ 
tial in the structural assignment. 

An exact mass was obtained of the nominal 
M/E=+208 using a VG-Micromass ZAB-2F 
operated in the positive ion-electron impact made. 
The resolution was 5,000 and the reference was the 
204.9888 ion of perfluorokerosene (PFK). The 
sample was introduced through the solid probe 
and heated only by the source which was set at 200 
degrees Celsius. The measured exact mass was 
208.6695 and the expected error in the measure¬ 
ment was ± l.Oppm. When the data sysem was 
consulted for possible atomic formula with C, H, 


N and O, only two possible formula fell within ex¬ 
perimental error; C 6 Hi 20 6 N 2 or C 5 IT.O 1 N 9 . The 
second was eliminated as a possibility because of 
the odd number of nitrogens, which made an even 
molecular weight unlikely if normal rules of val¬ 
ence were followed. The experiment was repeated 
using methane chemical ionization and peak 
matching the M/E = +205 ion of PFK to the 
M/E = +209 ion. The measured mass was 

209.0774 which also was consistant with atomic 
compositions C 6 H, 3 0 6 N 2 corresponding to (M + 
H) + . This data when taken together with the earli¬ 
er isotopic ratioing experiment performed on the 
quadrypole mass spectrometer strongly indicated 
that the molecular formula was C 6 H 12 0 6 N 2 . 

The 'H NMR was obtained from a solution of 
the powder dissolved in d 6 -DMSO. The spectrum, 
which appears in Figure 6 shows only a single 
weak AB system with a chemical shift of 4.3 ppm. 
The weak AB system was consistent with a mole¬ 
cule having only methylene groups in identical 
chemical environments. The chemical shift of 4.3 
ppm was quite unusual, and was not assigned at 
that time. 

Next, all the spectra were pooled, and structures 
were drawn until one was found that did not con¬ 
flict with the data (see Figure 7). The molecule, 
which is a bicyclic triperoxide with D 3 h symetry, 
was judged as an unlikely structure by many who 
viewed it, due to thermodynamic considerations. 
Consequently a l3 C NMR spectrum of the sample 
dissolved in d 6 -DMSO was obtained (see Figure 
8 A). The spectra clearly indicates one carbon with 
two hydrogens attached. The proton decoupled 
l3 C NMR spectra shown in Figure 8 B further rein¬ 
forces this interpretation. 

With the structural identification verified, a lit¬ 
erature search turned up several references to 
hexamethytentripexoride diamine (HMTD). 
Those references confirmed the solubility and 
physical data and showed that the potential as a 
commercial or military explosive was investigated 
as early as 1904. Those studies concluded that 
HMTD was too unstable for any commercial ap¬ 
plication. 

The explosive is of interest to forensic scientists, 
however, because of the obvious utility of HMTD 
for an unsophisticate terrorist. There are at least 
two synthesis routes for producing HMTD which 
require virtually no laboratory equipment and the 
starting chemicals that can be purchased quite in¬ 
conspicuously. The explosive can be detonated us¬ 
ing the crudest of initiators and has the same deto- 


151 














































SWEEP TIME: 5 min 
SWEEP WIDTH: 10PPM 
SOLVENT: DMSO-d 6 



Figure 6. 'H NMR spectrum of unknown explosive powder 


CHo- O* O-CHo 

/ X 

n«ch 0 -o-o-ch 9 wr 

\ 2 y 

ch 2 -o-o-ch 2 


Figure 7. Flexamethylenetriperoxidediamine 


152 














DMSO 


Scan Width: 4 KHz 

No. of Transients: 76. 701 
Aquisition Time: 1. 023 sec 




' I'M 


i—r~"r 


“i—i— r 


1 i 1 i 1 i 1 r 


IMS 



Figure 8-A. 13 C NMR spectrum of unknown explosive powder 



Figure 8 -B. ' 3 C NMR spectrum of unknown explosive powder: protons decoupled 


153 
































m 


Vv\ 


CQ 

CD 


ID 


UV: 254 nm 


I 

i 



CHROMATOGRAPHIC CONDITIONS: 
Flow: 2. 0 ml/min 
Column: 5 um Spherical Silica 
Injection Volume: lOul 
Mobile Phase: 30% Methylene Chloride 
70% Iso-Octane 


Thermal Energy 
Analyzer 


tr¬ 

io 


o 

0) 



0 


I I 

5 10 

Time(min) 


15 


I * ' • ■ i 

5 10 

Time (min) 


I 

15 


Figure 9. HPLC chromatogram of headspace sample from bombing debris 



154 





























nation velocity as TNT. The explosive itself is 
somewhat volatile and all the detonation products 
are a gas at room temperature. 

The second case was a terrorist bombing which 
occurred outside the contiguous 48 United States 
which resulted in considerable loss of human life. 
When the bombing debris reached the FBI Labo¬ 
ratory several pieces of soft material which were 
obvipusly near the point of detonation were 
placed in an air tight can and heated while the va¬ 
pors of the can were collected on charcoal. After 
an hour of collection, the charcoal was extracted 
with methylene chloride. The extract was concen¬ 
trated with a stream of nitrogen and injected with¬ 
out further preparation into the HPLC system 
which was described earlier. The trace from the 
UV detector, which was at maximum sensitivity, 
showed seven distinct peaks while the TEA 
showed two very strong peaks (see Figure 9). The 
retention times did not match those for EGDN, 
NG, TNT, DNT, PETN, RDX or HMX. The rela¬ 
tive responses recorded for the peaks appearing on 
the tw'o recorders and having the same retention 
(adjusted for the dead volume between the detec¬ 
tors) were indicative of nitrate esters. The same ex¬ 
tract was then analyzed by GC/MS. A cold, 
on-column injector was used to inject 1 ul of the 
extract onto a fused silica capillary column coated 
with bonded SE-54. The RIC for the El GC/MS 
run is shown in Figure 10. The El spectra of the 
first peak which appeared at scan 170 on the RIC 
appears in Figure 11. The data system searched the 
EPA-NIH library and found a good match for 
diethylene-glycol dinitrate (DEGDN). The El 
mass specta for the second component which ap- 



Figure 11. Electron impact (70 eV) mass spectra of first major 
component of headspace sample from bombing debris 


peared at scan 237 on the RIC is shown in Figure 
12. That spectrum is indistinguishable from the El 
mass spectrum of EGDN, NG and PETN. An¬ 
other GC/MS run was made using methane 
chemical ionization and the same GC conditions. 
The spectra for the first peak was consistent with 
one that would be expected for a nitrate ester with 
a molecular weight of 196 daltons, thus reinforc¬ 
ing the tenative identification of DEGN (see 
Figure 13). The Cl mass spectrum for the second 
eluting component which is shown in Figure 14 
was consistent with a mass spectrum for a nitrate 
ester with a molecular weight of 255 daltons. 

The residue remaining at this point contained 
approximately 10 ug of explosive total, as judged 
by the response on the HPLC-TEA for other ni¬ 
trate esters. The possibility of obtaining a useful 
infrared or NMR spectrum of either component 
seemed remote. With only DEGDN tenatively 
identified, identifying the original explosive would 
be impossible. 

The primary use of DEGDN is in propellants, 
especially some foreign made smokeless powders. 
The debris, however, was not indicative of smoke¬ 
less powder damage. The only possibility for 
identifying the explosive was in identifying the sec¬ 
ond component found in the headspace. It was de¬ 
cided that the only course left was to go through 
the available references on explosives page by page 
to locate a nitrate ester with a molecular weight of 
255 daltons. Metriol trinitrate (MTN) emerged as 
the most likely of the possibilities. 

There were no explosives in the FBI collection 
which contained both MTN and DEGDN. Since 
the bombing was by a terrorist outside the United 
States there was a strong possibility that the explo¬ 
sive was foreign made. An expert on foreign 
manufactured explosives was contacted who 
identified the most probable source as “Hercu- 
dyne,” a dynamite made by Hercules in the 
United States. Arrangements were made to get 
pure standards of MTN and DEGN from the 
manufacturer and those standards were run on the 
HPLC system and the GC/MS systems for com¬ 
parison (see Figures 15 and 16). A portion of the 
bombing debris extract was spiked with the two 
known explosives and rerun on both HPLC and 
GC/MS systems. The results of these comparative 
examinations strongly indicated that the explosive 
had been identified. 

These two cases demonstrated a significant 
shortcoming of the laboratory procedures used to 
solve them. All the materials identified in these 


155 









46 



Figure 12. Electron impact (70 eV) mass spectra of second major component of headspace sample from bombing debris 


105 



Figure 13. Methane chemical ionization mass spectra of first major component of headspace sample from bombing debris 


156 
















100 % 


193 



146 


256 


101 


130 


137 


162 176 


209 


M/Z 


100 


150 


I 

200 



301 

I 

300 


Figure 14. Methane chemical ionization mass spectra of second major component of headspace sample from bombing debris 



157 

























181 



Figure 16. Total ion chromatogram of a 50/50 mixture of metriol trinitrate (MTN) and diethyleneglycol dinitrate (DEGDN) 


cases were in standard references on explosives. 
The second explosive had been manufactured in 
this country for a number of years. However, 
none of the explosives were in the FBI’s extensive 
collection and no spectral data was recorded for 
those explosives in any of the standard spectra ref- 
ference libraries. There are hundreds of other ex¬ 
plosives which are listed in common references for 
which the same statement could be made. There is 


then a need to establish a comprehensive file of Cl 
mass spectra of explosives, for with this data the 
compounds discussed above could have been 
identified with relatively little effort. 

ACKNOWLEDGMENTS 

We would like to thank Dr. Sphon and Dr. Ma¬ 
zda of the FDA for their high resolution mass 
spectroscopy and NMR work. 


158 















DESCRIPTION OF A NITRO/NITROSO SPECIFIC 
DETECTOR FOR THE TRACE ANALYSIS OF 

EXPLOSIVES 


Goff, E. U. and Yu, W. C. 

Thermo Electron Corporation 
101 First Avenue 
Waltham, MA 02254 
U.S.A. 

Fine, D. H. 

New England Institute for Life Sciences 
125 Second Avenue 
Waltham, MA 02254 
U.S.A. 


ABSTRACT. A nitro/nitroso specific detector for both capillary column gas 
chromatography (GC-TEA) and high-performance liquid chromatography 
(HPLC-TEA) is described. The sensitivity of GC-TEA at a signal-to-noise ratio 
of 3/1, is approximately 5 pg for ethylene glycol dinitrate (EGDN), glycerol trini¬ 
trate (NG), 2,4-dinitrotoluene (2,4-DNT), 2,4,6-tinitrotoluene (TNT), 
cyclo-1,3,5 trimethylene-2,4,6 trinitramine (RDX) and 25 pg for trini- 
tro-2,4,6-phenylmethylnitramine (tetryl). The precision at the 1 ng level, expressed 
as relative standard deviations, was ±1.6% for EGDN, ±1.4% for NG, ± 2% for 
2,4-DNT, ±1.3% for TNT, ±5.7% for RDX and ±2.6% for tetryl. For 
HPLC-TEA, the precision at the 1 ng level for NG, isosorbide dinitrate (ISDN) 
and pentaerythritol tetranitrate (PETN) was ±2.3%, ±8.6% and ±5.9% relative 
standard deviations respectively. The linearity of the instrument response from 
0.1-50 ng range has been demonstrated using NG, PETN, and ISDN, with correla¬ 
tion coefficients of 0.9942, 0.9963 and 0.9841, respectively. Confirmation of the 
identity of the compound under test is achieved by the use of parallel GC-TEA and 
HPLC-TEA analysis. 


INTRODUCTION 

A variety of techniques have been used for the 
analysis of explosives. Some of the most com¬ 
monly used techniques, such as thin layer chrom¬ 
atography (Douse, 1982; Kempe and Tannert, 
1972; Peak, 1980; Twibell et at., 1982; Yinon and 
Zitrin, 1981) polarography (Hetman, 1973; Whit- 
nack, 1975; Yinon and Zitrin, 1981), ultraviolet 
(Baaske et al. , 1983; Doali and Juhasz, 1974; Dal¬ 
ton et al., 1975; Gelber and Papas, 1983; Krull 
and Camp, 1980; Yinon and Zitrin, 1981) and in¬ 
frared spectroscopy (Meyers, 1977; Peimer et al., 
1980; Washington, 1976; Yinon and Zitrin, 1981) 
require large sample quantities and, in some cases, 
extensive clean-up procedures to minimize the in¬ 
terference problems and positively identity the un¬ 


known explosives. The gas chromatography-elec¬ 
tron capture technique (GC-ECD) provides a sen¬ 
sitive method for the analysis of explosives but 
suffers from detector overloading and contamina¬ 
tion, and subsequent loss of sensitivity and linear¬ 
ity during the analysis of environmental samples 
unless great care is taken with respect to sample 
clean-up (Douse, 1981; Douse, 1982; Twibell et 
al., 1982; Yinon and Zitrin, 1981). Chemical ioni¬ 
zation mass-spectroscopy (CIMS), in conjunction 
with electron impact mass-spectroscopy (EIMS), 
has been used successfully for the positive identifi¬ 
cation of explosive compounds (Mach et al., 1978; 
Yinon and Zitrin, 1977). Negative ion CIMS of ex¬ 
plosives provides excellent sensitivity and selectiv¬ 
ity for the detection of these compounds (Yinon 


159 


and Zitrin, 1981; Yinon, 1980). The on-line use of 
HPLC in conjunction with C1MS is a very selec¬ 
tive method but lacks sensitivity because LC/MS 
interface only allows about 1% of the sample into 
the ion source (Parker et al., 1982). Also, the high 
cost of the mass-spectroscopic techniques limits 
the widespread use of this approach. 

In this report, we describe a nitro/nitroso spe¬ 
cific detector, called the TEA analyzer, for the 
rapid, sensitive and selective determination of ex¬ 
plosive residues. The TEA itself, and its detailed 
principle of operation, has been described pre¬ 
viously (Fine et al ., 1975; Fine et al., 1975; 
LaFleur and Mills, 1981; LaFleur and Morriseau, 
1980). A brief description will be given in the “Ex¬ 
perimental” section of this paper. 

EXPERIMENTAL 

Reagents 

All solvents used were of distilled-in—glass 
grade (Burdick and Jackson). The explosives used 
in this study were glycerol trinitrate (NG), pen- 
taerythritol tetranitrate (PETN), isosorbide dini¬ 
trate (ISDN), ethylene glycol dinitrate (EGDN), 
2,4-dinitrotoluene (2,4-DNT), 2,4,6-trinitroto¬ 
luene (TNT), cyclo-l,3,5-trimethylene-2,4,6- 
trinitramine (RDX), trinitro-2,4,6- 
phenylmethylnitramine (Tetryl). 

GC-TEA 

A gas chromatograph (Hewlett Packard, Model 
5840A), equipped with an on-column injector 
(SGE Scientific, Model OCI-3) was used. The 
fused-silica capillary column (DB-5) was 30 m 
long, 0.32 mm i.d. and had a 0.25 um film thick¬ 
ness. The carrier gas was helium at a head pressure 
of 18 psi. The injection port temperature was am¬ 
bient. For the separation of the explosives shown 
in Figure 2, the oven temperature was held at 60 °C 
for 1 minute, and then increased at 15°C/minute 
to 240°C, and then held at 240°C for 3 minutes. 
For the separation of the explosives shown in Fig¬ 
ure 3, the oven temperature was programmed 
from 40°C to 200°C at a 10°C/min. rate. 

The detector was a TEA analyzer (Thermo Elec¬ 
tron, Model 610), operating in the nitro mode. 
The interface temperature was 285 °C, and the 
pyrolyzer temperature was 900 °C. The reaction 
chamber was held at 1.8 mm Hg, with an 0 3 flow 
of 5 ml/minute. The cold trap was maintained at 
-100°C with a slush bath of ethanol and liquid 
nitrogen. The amount of material injected on col¬ 
umn was 0.2 ul - 1.0 ul. 


HPLC-TEA 

The high-performance liquid chromatographic 
system consisted of a solvent pump (Altex, Model 
110) and an injector (Waters Associates, Model 
U6K). The column was a 10 um uBondapak CN, 
30 cm long by 3.9 mm i.d. (Waters Associates). 
For screening EGDN, TNT, NG, PETN, and 
RDX, the solvent system was isooctane/methylene 
chloride/methanol in the ratio 165/35/10. The 
solvent flow rate was maintained at 1.5 ml/min¬ 
ute. Typically, the amount injected, on column, 
was 5-10 ul. The TEA catalytic pyrolyzer was op¬ 
erated at 550°C. The reaction chamber vacuum 
was 1.8 mm Hg, with an 0 3 flow rate of 5 ml/min¬ 
ute. The carrier gas was N 2 , at a flow rate of 20 
ml/minute. The TEA cryogenic trap was main¬ 
tained at -78°C with a slush bath of ethanol and 
solid carbon dioxide. 

DESCRIPTION OF THE TEA ANALYZER 

The effluent from the chromatograph enters a 
catalytic pyrolyzer, where NO? is released from 
organic nitro compounds and simultaneously con¬ 
verted into NO by the catalytic surface. Solvent 
vapors and pyrolysis products are then removed 
by a cold trap which is maintained at about 
- 100°C. The NO gas which survives the trap is 
reacted with ozone (0 3 ) in the reaction chamber at 
reduced pressure to produce the characteristic in¬ 
frared chemiluminescent reaction, the intensity of 
which is monitored by an infrared-sensitive 
photomultiplier tube (Figure 1). While the tech¬ 
nique is sensitive at the picogram level, it is also 
highly selective. The rejection ration of the TEA 
to hydrocarbons and N-containing organics is 
greater than 10 6 to 1 (Fine et al, 1975). A partial 
list of compounds which have been shown to give 
no response on the TEA is shown in Table 1. The 
selectivity stems from four factors. First, only 
compounds which have the N0 2 or NO functional 
groups can give a response. Second, the reactive 
species must survive the - 100°C cold trap. For 
highly contaminated samples, a - 160°C trap can 
be used. Third, the reactive species must react with 
0 3 to produce a chemiluminescent light in the nar¬ 
row wavelength range of 0.6-2.8 microns. Fourth, 
the reaction with 0 3 must be rapid enough to oc¬ 
cur while the effluent is in the reaction chamber, 
and not in the vacuum pump. 

RESULTS AND DISCUSSION 

Separation of the various explosives on GC and 
HPLC were developed. Figure 2 shows the injec- 


160 


PRINCIPLE OF OPERATION 
Nitro Compounds 



X N —N0 2 

^c-no 2 ) 
_o— no 2 






PYROLYSIS 


350M000°C 


^ N 

7 C ' 
_ O' 


NO* + O 3 -N0 2 + 0 2 

* N0 2 N0 2 -N0 2 + hU AT 600 nm 


•no 2 


PYROLYSIS 

* NO- + 1/20 2 
350°-1000°C 


Figure 1. Principle of operation of the TEA Analyzer for nitro compounds. 


tion of six common explosives—EGDN, NG, 
2,4-DNT, TNT, RDX, and Tetryl at approx¬ 
imately 1 ng level on capillary GC-TEA. Under 
the GC conditions used, all six compounds were 
baseline resolved. For the separation of NG, 
2,4-DNT, TNT, PETN and RDX, as shown in 
Figure 3, a slightly different chromatographic 
condition needs to be used to resolve PETN from 
TNT and RDX. Also, a reduced response for 
PETN on GC-TEA was observed due to the de¬ 
composition of the cmpound on the chromato¬ 
graphic system before it reaches the detector. This 
same phenomenon was also observed by Douse 
(1982) when an electron capture detector was 
used. Apparently, even under the ambient injec¬ 
tion conditions, the lability of PETN limits the 
GC approach for detecting this compound. 

Since liquid chromatography operates on a dif¬ 
ferent set of parameters than gas chromatogra¬ 
phy, and it is amenable to thermally unstable com¬ 
pounds, the HPLC-TEA technique offers a com¬ 
plimentary approach to GC-TEA. LaFleur and 
Morriseau (1980) have already demonstrated the 


detection of various explosives by HPLC-TEA us¬ 
ing solvent programming techniques. 

For the routine screening of a large number of 
samples for explosive residues, an isocratic condi¬ 
tion might be more practical. Using a uBondpak 
CN column, we can separate EGDN, TNT, NG, 
PETN and RDX by HPLC-TEA, as shown in Fig¬ 
ure 4. By increasing the polarity of the mobile 
phase, one can also screen for HMX. Thus, for 
thermally labile compounds such as PETN and 
HMX, HPLC-TEA can be used. 

Sensitivity. 

The sensitivity attainable on the capillary col¬ 
umn GC-TEA is demonstrated by the three 
chromatograms shown in Figure 5. Figure 5A is 
the chromatogram for 10 pg of NG, 8 pg of TNT 
and 7 pg of RDX, introduced on column. The 
three peaks are clearly discernible above the back¬ 
ground. The minimum detectable level at a sig- 
nal-to-noise ratio of 3/1, is estimated to be 4 pg 
for TNT and RDX, 5 pg for EGDN, NG and DNT 
and 25 pg for tetryl. Although the chromatograms 


161 


























Figure 2. Analysis of six explosives on capillary column 
GC-TEA (Attenuation x 32). Peak identification is as follows. 
Peak 1-1.2 ng EGDN, Peak 2-0.8 ng NG, Peak 3-1.1 ng 
2,4-DNT, Peak 4-1.3 ng TNT, Peak 5-1.0 ng RDX, Peak 
6-1.7 ng Tetryl. 


of Figure 5 were obtained with standard solutions, 
little degradation in performance is observed when 
analyzing complex explosive residue samples. 

Precision. 

For the HPLC-TEA, precision data has been 
demonstrated using NG, PETN and ISDN, at the 
1 ng, 5 ng, 20 ng and 50 ng level injected on col¬ 
umn (Yu and Goff, 1983), as shown in Table 2. At 
the 1 ng injection level, for example, the relative 
standard deviations were ±2.3% for NG, ±5.9% 
for PETN and ±8.6% for ISDN. For capillary 
column GC-TEA, the precision, expressed as rela¬ 
tive standard deviations, which was attained over 
5 injections of approximately 1 ng on column, was 
±1.6% for EGDN, ±1.4% for NG, ±2% for 
2,4-DNT, ±1.3% for TNT, ±5.7% for RDX 
and ± 2.6% for tetryl (Table 3). 



PEAK IDENTIFICATION: 
(7) NC, 1.0 ng 
Q) 2,4-DNT, 1.0 ng 
(7) TNT, 0.8 ng 

© PETN, 1.0 ng 
© RDX, 1.2 ng 


Figure 3. Analysis of five explosives on capillary column, 
GC-TEA. Peak identification is as follows. Peak 1-1.0 ng NG, 
Peak 2-1.0 ng 2,4-DNT, Peak 3-0.8 ng TNT, Peak 4-1.0 ng 
PETN, Peak 5-1.2 ng RDX. 


Linearity. 

The detector has been shown to be linear over 6 
orders of magnitude (Fine et al, 1975). LaFleur 
and Morriseau (1980) also demonstrated the lin¬ 
earity of the detector response as a function of 
concentration for RDX and PETN (Figure 6). The 
points were obtained by ten determinations at 
each of the three concentration levels. For RDX, 
the concentration levels were 219, 2190 and 21900 
ng/mL. For PETN, the concentration levels were 
320, 3120 and 31200 ng/mL. The linearity of re¬ 
sponse as indicated by the correlation coefficients 
was greater than 0.999. The linearity of the detec¬ 
tor has also been demonstrated as a function of 
the number of nitrosyl-containing functional 
groups per molecule for nitrate esters and nitra- 
mines (Figure 7). For the nitrate esters (com¬ 
pounds with -ON0 2 functional groups), the 
compounds used were isosorbide-5-mononitrate 
(5-ISMN), ISDN, (two -ON0 2 ) NG (three 
-ON0 2 ) PETN (four -ON0 2 ). For nitramines, 
1-nitroguanidine; RDX (a trinitramine) and HMX 
(a tetranitramine) were used. For each compound 
ten determinations were performed. The linearity 
of both plots, expressed as correlation coeffi¬ 
cients, was greater than 0.99. 


162 


































Figure 4. Analysis of five explosives by HPLC-TEA (Atten¬ 
uation x 16). Peak identification is as follows. Peak 1-8.0 ng 
EGDN, Peak 2-64 ng TNT, Peak 3-8.0 ng NG, Peak 4-8.0 ng 
PETN, Peak 5-8.0 ng RDX. 

In this paper we establish the linearity for NG, 
ISDN and PETN from 0.1-50 ng with the corre¬ 
sponding linear regression correlation coefficients 
of 0.9942, 0.9841 and 0.9963, respectively (Figure 
8). Quadruple determinations were made for each 
point. 

Parallel GC-TEA/HPLC-TEA Confirmation. 

The operation of a selective detector with both 
GC and HPLC offers a novel self-confirmatory 
capability. In GC, separation of the compounds is 
achieved by differences in vapor pressure and sol¬ 
ubility in the liquid phase of the column. In 
HPLC, however, polarity, physical size, and 
shape characteristics determine the chromato¬ 
graphic selectivity. The result is that the elution 
order of the explosives is different on GC and on 
HPLC. Thus, an analysis which is highly specific 
could be interpreted as confirmatory by an ex¬ 
aminer if three criteria are met: 


(i) The peak elutes at the proper retention time 
on both GC-TEA and HPLC-TEA. 

(ii) Both chromatograms are relatively clean. 

(iii) Identical quantitation is achieved on both 
systems. 

If some doubt exists because of multiple peaks, 
the compound can be isolated off HPLC-TEA by 
collecting the effluent at the retention time indi¬ 
cated by a previous HPLC-TEA run before the 
compound enters the pyrolyzer, concentrated and 
reinjected on both HPLC-TEA and GC-TEA. A 
single peak of the proper quantitation eluting at 
the proper retention time, can be taken as con¬ 
firmatory. Data, based on this principle, are pre¬ 
sented in the following paper (Fine, et al ., 1983). 
Parallel GC-TEA/HPLC-TEA determinations 
have been used successfully in the N-nitrosamine 
field, when the amount of sample was too small to 
be handled by other methods (Fine 1980, Fine et 
al., 1977) and have been interpreted by workers in 
that field as confirmatory. 


CONCLUSION 

The sensitivity of the TEA analyzer for explo¬ 
sive analysis in the low picogram (pg) range has 
been demonstrated. This sensitivity level is main¬ 
tained even when analyzing complex samples be¬ 
cause of the unique selectivity of the detector. The 
advantages of using a selective detector are sever¬ 
al. Aside from the benefits of excellent sensitivity, 
the need for extensive sample clean-up procedures 
prior to sample analysis is eliminated, with subse¬ 
quent savings in the time spent for sample prepa¬ 
rations and material costs. 

The parallel use of HPLC-TEA and GC-TEA 
techniques increases the selectivity of the detector 
and serves as a confirmatory approach. 

The linearity of detector response in the low pg 
and nanogram (ng) range renders the TEA tech¬ 
nique suitable for the sub part per billion (ppb) 
level determinations of explosives in post-blast de¬ 
bris, handswabs, wastewater effluents, air sam¬ 
ples, and human plasma. The practical application 
of this technique will be presented in the following 
papers. 


ACKNOWLEDGEMENTS 

We thank D. Reutter of the FBI for many val¬ 
uable discussions. The technical assistance of J. 
Buckley is gratefully acknowledged. 


163 




















Peak 


(T) NG 

@ TNT 
(3) RDX 


Amount 

A. 

10 

8 


Injected 

B. 

20 

16 

14 


Picograms 

C. 

50 

40 

35 


A. 





J_I_L 

0 3 6 

TIME 

(Minutes) 


B. 


C. 



0 3 6 


TIME 

(Minutes) 



Figure 5. Sensitivity of capillary column GC-TEA, for 0.2 ul injection of NG (Peak 1), TNT (Peak 2), and RDX (Peak 3). 


164 
























DETECTOR RESPONSE AS A FUNCTION 
OF CONCENTRATION FOR PETN AND RDX 

LOG q [AMOUNT INJECTED (ngf) 



LOG |0 [CONC. ( ng / mL)] 


DETECTOR RESPONSE VS THE NUMBER OF 
NITROSYL-CONTAINING FUNCTIONAL 
GROUPS PER MOLECULE 



- £ S I-1-1_L 

0 12 3 4 


NITROSYL GROUPS (MOLE NO ) 

Figure 7. TEA Analyzer linearity response, demonstrated as a 
function of the number of nitrosyl-containing functional 
groups per molecule. Nitrate esters (with -0N0 2 group) and 
nitramines (with NN0 2 groups) were employed. 


Figure 6. TEA Analyzer linearity response for PETN and 
RDX. PETN concentration levels were 219, 2190 and 21900 
ng/ml. RDX concentration levels were 320, 3120, and 31200 
ng/ml. 


TABLE 1. REPRESENTATIVE LIST OF COMPOUNDS WHICH WERE FOUND TO 
GIVE NO INTERFERENCE ON THE TEA 


Acetic acid 

Ethyl acetate 

Oxalic acid 

Acetone 

Ethyl carbamate 

n-Pentane 

Acetonitrile 

Ethylene glycol 

Phenyl hydrazine 

Alizarin red 

Fluorobenzene 

d,1-Phenylalanine 

Ammonia (gas) 

Gasoline 

p-Phenylazoaniline 

Benzene 

Glycerol 

Phosphoric acid 

Benzylsalicylate 

d-Glucose 

Propane (gas) 

2-Butoxy ethanol 

Glutamic acid 

Pyridine 

Carbon dioxide 

n-Hexane 

Quinine 

Carbon disulfide 

Hydrogen (gas) 

Sodium acetzolamide 

Carbon monoxide (gas) 

Hydroquinone 

Sulfadiazine 

Carbon tetrachloride 

8 -Hydroxyquinoline 

Sulfanilic acid 

Chloral hydrate 

I nosine 

Tetrahydrofuran 

Chlorobenzene 

d,1-iso-leucine 

Theophylline 

1-Chloropropane 

Methane (gas) 

Toluene 

2-Chloropropane 

Methyl acetate 

2,4,6-Trichlorophenol 

Cyclohexane 

N-Methyl bisacrylamide 

2,2,4-T rimethylpentane 

Cyclopentane 

2-Methyl butane 

d,1-Tryptophane 

1,2-Dichloroethane 

Methyl formamide 

Urea 

2,3-Dichloropropane 

Methyl isobutyl ketone 

Uric acid 

Diethylether 

Methyl orange 

Urethane 

Dimethylamine (gas) 

Methyl red 

Water 

p-Dioxane 

Napthalene 

Xylene 

Diphenylamine 

Nitrogen (gas) 



165 





TEA Analyzer Linearity Response for' 

(a) NG 

(b) PETN 

(c) ISDN 

Figure 8. TEA Analyzer linearity response for NG, PETN, ISDN at 0.1-50 ng range. 


TABLE 2. PRECISION OF HPLC-TEA 


Compound 

Amount 

Injected 

ng 

Response 

(X)« 

(S)b 

(SrK 

NG 

1.0 

5.28 x 105 

0.12 

2.3 


5.0 

2.77 x 106 

0.11 

4.1 


20.0 

1.16 x 10? 

0.04 

3.5 


50.0 

2.65 x 10’ 

0.09 

3.4 

ISDN 

1.0 

1.41 x 105 

0.12 

8.6 


5.0 

8.25 x 105 

0.61 

7.3 


20.0 

3.25 x 106 

0.21 

6.5 


50.0 

1.62 x 10’ 

0.12 

7.4 

PETN 

1.0 

4.41 x 105 

0.25 

5.9 


5.0 

2.04 x 106 

0.04 

2.2 


20.0 

7.85 x 106 

0.34 

4.3 


50.0 

2.08 x 10’ 

0.05 

2.4 


a (X) = MEAN VALUE FOR 5 DETERMINATIONS, ARBITRARY UNITS. 
b (S) = STANDARD DEVIATION. 

c (Sr) = RELATIVE STANDARD DEVIATION EXPRESSED AS A PERCENT. 


166 









TABLE 3. PRECISION OF CAPILLARY GC-TEA ON EXPLOSIVES AT THE NANOGRAM LEVEL 

(n = 5) 


Compound 

Amount 

Injected 

n 8 

Integrated 

Area 

Std. 

Dev. 

% 

Rsd 

EGDN 

1.2 

1.80 x 10“ 

0.03 

1.6 

NG 

0.8 

1.51 x 10“ 

0.02 

1.4 

2,4-DNT 

1.1 

1.14 x 10“ 

0.02 

2.0 

TNT 

1.3 

1.88 x 10“ 

0.02 

1.3 

RDX 

1.0 

1.31 x 10“ 

0.07 

5.7 

TETRYL 

1.7 

1.07 x 10“ 

0.03 

2.6 


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Kempe, C. R., Tannert, W. K. (1972). Detection 
of dynamite residues on the hands of bombing 
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plosives by HPLC. Amer. Lab 12: 63-76. 

LaFleur, A. L. and Morriseau (1980). Identifica¬ 
tion of explosives at trace levels by high-per¬ 
formance liquid chromatography with a 
nitrosyl-specific detector. Anal. Chem. 
52: 1313-1318. 

LaFleur, A. L. and Mills, K. M. (1981). Trace lev¬ 
el determination of selected nitroaromatic com¬ 
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53: 1202-1205. 

Mach, M. H., Pallos, A., and Jones, P. F. (1978). 
Feasibility of gunshot residue detection via its 
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metry. J. Forensic Sci. 23: 433-445. 


167 








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Parker, C. E., Voyksner, R. D., Tondeur, Y., 
Henion, J. D., Harvan, D. J., Hass, J. R., and 
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25: 679-681. 

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plosive, C-4 J. Forensic Sci. 25: 398-400. 

Twibell, J. D., Home, J. M., Smalldon, K. W., 
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Drug Disp. 


168 


APPLICATIONS OF THE NITRO/NITROSO SPECIFIC 
DETECTOR TO EXPLOSIVE RESIDUE ANALYSIS 


Fine, D. H. 

New England Institute for Life Sciences 
125 Second Avenue 
Waltham, MA 02254 
U.S.A. 

Yu, W. C. and Goff, E. U. 
Thermo Electron Corporation 
Waltham, MA 02254 
U.S.A. 


ABSTRACT. The specificity of the TEA® Analyzer interfaced to a gas chroma¬ 
tograph (GC-TEA) and/or a liquid chromatograph (HPLC-TEA) renders the 
technique a useful tool for the analyses of explosive residues in a wide variety of 
forensic and environmental applications. Specific applications to the analyses of 
explosive residues are described, including post-explosion debris and washings 
from persons who have handled explosives. Examples of environmental data are 
also included. 


INTRODUCTION 

The ideal technique for the ultra-trace analysis 
of explosives would be both simple and rapid, re¬ 
quire minimal sample clean-up, be sensitive to as 
little as 1-10 pg (picograms, lCT ]: g) quantities of 
all the compounds of interest, and would work 
equally well on both complex samples from the 
real world and on high-grade laboratory stand¬ 
ards made up in pure solvents. The TEA Analyzer 
has been designed to respond only to nitro- and 
ntroso-containing compounds. Its principle of 
operation was presented in detail in the previous 
paper by Goff et al. (1983). The practical applica¬ 
tion of the detector in the forensic science area will 
be discussed here. 

The possible application of the TEA analyzer to 
the problem of the analysis of organic nitro com¬ 
pounds has been addressed recently by LaFleur 
and Mills (1981) Maddock et al. (1983), Phillips et 
al. (1983) and Yu and Goff (1983, a,b). The per¬ 
formance of the TEA analyzer as a detector for 
explosives in high-performance liquid chroma¬ 
tography and gas chromatography has been de¬ 
scribed by LaFleur and Morriseau (1980), and 
LaFleur and Mills (1981), respectively. Three 
laboratories have developed procedures for the 
routine analysis of nitrate esters such as NG, 


ISDN and PETN in blood at levels as low as 100 
pg/ml. A comparison of the TEA analyzer with 
three other GC detectors; electrolytic conductiv¬ 
ity, thermionic and electron capture, has been 
made by Phillips et al (1983) for the analysis of 
nitroaromatics such as nitrobenzene, and the dini- 
trotoluenes in sludge wastes. Douse (1983) recent¬ 
ly demonstrated the low picogram detection of 
explosives using silica capillary column gas 
chromatography with a TEA analyzer. This paper 
expands the applicability of the TEA analyzer for 
trace explosive residue analysis, to the low pico¬ 
gram level, on real world samples such as pieces of 
explosives, post-blast residues and handswabs. It 
is also shown that by using parallel HPLC-TEA 
and GC-TEA techniques it is possible to confirm 
the identity of the compound if the confirmatory 
criteria described in the preceding paper are met. 

EXPERIMENTAL PROCEDURES 
Reagents 

All solvents were of a grade which had been dis¬ 
tilled in glass (Burdick and Jackson). The explo¬ 
sives used in this study were glycerol trinitrate 
(NG), pentaerythritol tetranitrate (PETN), ethyl¬ 
ene glycol dinitrate (EGDN), 2,4-dinitrotoluene 
(2,4-DNT), 2,4,6-trinitrotoluene (TNT), cyclo-1, 


169 


3,5-trimethylene-2,4,6-trinitramine (RDX), trini- 
tro-2,4,6-phenylmethyl-nitramine (Tetryl), and 
cyclotetramethylene tetranitramine (HMX). 

SAMPLE PREPARATION 
a. Explosives. 

Small pieces of military and commercial explo¬ 
sives were dissolved in acetone to a concentration 
of 1 %. The samples were then diluted in methanol 
to obtain a 10 ppm (weight/volume) solution. No 
clean-up was used. 

B. Post-blast debris. 

Post-blast debris was collected from three test 
bombs (TNT, C4, and detonating cord), which 
were detonated by the FBI at the U.S. Marine 
demolition range at Quantico during January 
1983. The bombs were made by placing the explo¬ 
sive inside a 40-gallon metal trash can, with a 
stone weight on the lid. Blasting caps, equipped 
with a safety fuse, were used to detonate the de¬ 
vices. For TNT, a 1 lb. demolition block was used; 
for C4, a 1 14 lb. charge; and for the detonating 
cord alone, about 15 feet was wrapped around the 
can. After detonation, about 500 g of debris in¬ 
cluding metal fragments, soil and fabric were col¬ 
lected and sent to Thermo Electron for analysis. 

About 50 g of assorted debris was placed in a 
beaker (the metal fragments had to be cut so that 
they would fit into the beaker). After sonication in 
methylene chloride for 10 minutes, the methylene 
chloride was concentrated to 15 ml on a rotary 
evaporator, filtered through a Millex-SR filter 
and then concentrated under a stream of N 2 gas to 
2 ml. Aliquots were then analyzed by both 
GC-TEA and HPLC-TEA. 

C. Post-blast air sample. 

A Thermosorb/N (Thermo Electron) N-nitro- 
samine air sampling cartridge developed by Roun- 
behler et al (1980) was evaluated for its capability 
of trapping post-blast air samples. Following the 
detonation of a dynamite bomb at the FBI Quan¬ 
tico demolition range in April, 1982, 10 liters of 
air was drawn through a cartridge with a bicycle 
pump. The cartridge was capped and sent to 
Thermo Electron for analysis. 

The Thermosorb/N cartridge was analyzed in 
the conventional manner by eluting with 1.8 ml 
of methylene chloride/methanol (75/25) into a 
sample vial. The solution was then analyzed by 
HPLC-UV-TEA on a uBondapak CN column, 
using a solvent system of isooctane/methylene 


chloride/methanol (75/20/5) at a flow rate of 1.5 
ml/minute. 

D. Handswab experiments. 

The following were used for the test: C-4, gel 
dynamite, a plastic explosive and a piece of a letter 
bomb. Four volunteers held a small piece of explo¬ 
sive (approximately 1 x 3 cm) in the hand for 1 
minute. After 15 minutes, the palm area was 
washed twice with a cotton swab soaked in ace¬ 
tone, a proven technique used by Douse (1982), 
Twibell et al (1982 a,b). The swabs were squeezed 
to dryness, and the acetone washings were then 
analyzed directly. Aliquots were then analyzed by 
GC-TEA and HPLC-TEA. 

GC-TEA 

A gas chromatograph (Hewlett Packard, Model 
5840A), equipped with an on-column injector 
(SGE Scientific, Model OCI-3) was used. The 
fused silica capillary column (DB-5) was 30 m 
long, 0.32 mm i.d. and had a 0.25 urn film thick¬ 
ness. The carrier gas was helium at a head pressure 
of 18 psi. The injection port temperature was am¬ 
bient. The oven temperature was held at 60 °C for 
1 minute, and then increased 15°C/minute to 
240°C, and then held at 240°C for 3 minutes. The 
detector was a TEA analyzer (Thermo Electron, 
Model 610), operating in the nitro mode. The in¬ 
terface temperature was 285 °C, and the pyrolyzer 
temperature was 900°C. The reaction chamber 
was held at 1.8 mm Hg, with an 0 3 flow of 5 
ml/minute. The cold trap was maintained at 
-100°C with a slush bath of ethanol and liquid 
nitrogen. The amount of material injected on 
column was 0.2 ul - 1.0 ul. 

HPLC-TEA 

The high-performance liquid chromatographic 
system consisted of a solvent pump (Altex, Model 
110) with an injector (Waters Associates, Model 
U6K). The column was a 10 urn uBondapak CN, 
30 cm long by 3.9 mm i.d. (Waters Associates). 
For most of the work, two detectors, connected in 
series, were used. The column effluent flowed first 
through a variable wavelength UV detector, set at 
254 nm (Schoeffel, Model 770) and then into a 
TEA analyzer (Thermo Electron, Model 510). 
Some of the data were collected with only the TEA 
analyzer. For screening 2,4-DNT, EGDN, TNT, 
NG, PETN, tetryl and RDX, the solvent system 
was isooctane/methylene chloride/methanol in 
the ratio 165/35/10. For screening NG, PETN, 
RDX and HMX, the ratio of solvents was 


170 


60/30/10. The solvent flow rate was maintained at 
1.5 ml/minute. Typically, the amount injected, on 
column, was 25 ul. The TEA catalytic pyrolyzer 
was operated at 550°C. The reaction chamber 
vacuum was 1.8 mm Hg, with an 0 3 flow rate of 5 
ml/minute. The TEA carrier gas was N : , at a flow 
rate of 20 ml/minute. The TEA cryogenic trap 
was maintained at -78°C with a slush bath of 
ethanol and solid carbon dioxide. 

RESULTS AND DISCUSSION 
Explosives 

Parallel GC-TEA and HPLC-TEA chromato¬ 
grams are shown in Figure 1 for a sample of gela¬ 
tin dynamite, and in Figure 2 for double-based 
smokeless rifle powder. The dynamite sample gave 
only two peaks, one due to NG and the other to 
EGDN. The double-based smokeless powder 
sample gave only a single peak, due to NG. Con¬ 
stituents other than the explosive components 
(such as plasticizer) did not interfere with either 


the GC-TEA or HPLC-TEA analyses. 

Figure 3 is the HPLC-UV-TEA chroma¬ 
tograms for C-4, Flex-X and a sample cut from a 
defused letter bomb of Middle East origin. For 
C-4, RDX is the major peak, with a small amount 
of HMX also being present. Flex-X, was shown to 
contain only PETN. PETN was also the only 
explosive found to be present in the letter bomb. 

Although all five samples undoubtedly con¬ 
tained a multitude of materials other than the 
explosive constituents (plasticizers, etc.), no ex¬ 
traneous peaks were observed, even though no 
clean-up was used prior to analysis. It should be 
noted that although the UV detector is capable of 
far greater sensitivity at lower wavelengths, this 
high sensitivity is achievable only for standards. In 
all the data reported here, which include plasti¬ 
cizers etc., the greater sensitivity of the lower 
wavelengths is more than offset by the poor selec¬ 
tivity. Thus on an extract of a ‘real’ explosive, the 
peak due to the explosive would be drowned by 
the peak due to the impurities. 



GC-TEA (X 1 6) 



TIME (MINUTES) 
-HPLC-TEA (X64) 


Figure 1. Chromatograms on GC-TEA, and HPLC-UV-TEA 
of a 10 ppm extract from gelatin dynamite. GC-TEA was ob¬ 
tained with 1 ul injection, with peak 1 being 0.65 ng ot EGDN 
and peak 2 due to 0.25 ng of NG. For HPLC, 20 ul was in¬ 
jected on column. The EGDN peak was 13 ng, and the NG 
peak was 4.9 ng. 



TIME (MINUTES) 
CC-TEA (x 16) 


HPLC-UV 

254 nm, 0. 02 AUFS 



-J L 1 1|| 

0 2 4 6 8 10 
TIME (MINUTES) 
HPLC-TEA (X64) 


Figure 2. Chromatograms of GC-TEA and HPLC-UV-TEA 
of 10 ppm extract of double-based smokeless rifle powder. For 
GC-TEA, a 0.5 ul injection was used, with the NG peak due to 
1 .1 ng of NG. For HPLC-TEA, 7 ul was injected, with the NG 
peak being 15 ng. 


171 




































C. LETTER BOMB 


A. C-4 



B. FLEX-X 



0 4 8 12 

TIME (MINUTES) 



0 4 8 12 


TIME (MINUTES) 


Figure 3A. Chromatogram on HPLC-UV-TEA for 10 ul injection of a 10 ppm extract of C4. Peak 1, at the retention time of 
RDX, was 117 ng. Peak 2, due to HMX, corresponds to 4.2 ng. 3B. Chromatogram on HPLC-UV-TEA for 3 ul injection of a 10 
ppm extract of Flex-X. The single peak was due to 38 ng of PETN. 3C. Chromatograms on HPLC-UV-TEA for 5 ul injection of a 
10 ppm extract of a letter bomb. The single peak was due to 33 ng of PETN. 


Post-blast Debris 

From the chromatogram of the extract of the 
TNT bomb (Figure 4), the TNT component of the 
total explosive residue was determined to be only 
0.3%. On GC-TEA, the amount present in a 1 ul 
injection of the debris extract was 0.1 ng EGDN, 
4.4 ng NG, 0.15 ng 2,4-DNT, 0.03 ng TNT and 
0.5 ng RDX. 

For the detonating cord debris, (Figure 5), the 
GC-TEA showed a trace of EGDN, and a consid¬ 
erable amount of NG. The HPLC-TEA showed 
NG, as well as a trace of PETN (PETN partially 
decomposed in the GC). For debris from the C-4 


bomb (Figure 6), 9 ng of RDX, 7.8 ng of PETN 
and 5 ng of NG were found in a 20 ul injection on 
HPLC-TEA. Presumably, the cross contamina¬ 
tion of all three samples was from the Quantico 
demolition range itself, which had been in con¬ 
tinuous use for over 40 years. 

The data in Figures 4-6 demonstrate the cap¬ 
ability of the TEA analyzer in identifying 
post-blast explosive debris at the picogram level, 
even when the only sample preparation was ex¬ 
traction of the organic residue into a suitable sol¬ 
vent. Again, clean-up was unnecessary since there 
were few interfering peaks. 


172 








































TIME (MINUTES) TIME (MINUTES) 

CC-TEA HPLC-TEA 

Figure 4. Chromatograms on GC-TEA and HPLC-TEA of 
extracts from post blast debris following an explosion of a 
TNT bomb. On GC-TEA ( x 16), a 0.5 ul injection of debris 
extract gave 4.4 ng of NG, 0.15 ng of 2,4-DNT, 0.03 ng of 
TNT and 0.5 ng of RDX. For HPLC-TEA ( x 32) a 20 ul injec¬ 
tion was used. 


Post-blast Air Sample 

The TEA chromatogram, shown in Figure 7, 
shows the presence of EGDN, which is character¬ 
istic of a dynamite blast. The minimum detectable 
level of EGDN is less than the 9 ng shown in Fig¬ 
ure 7. The minimum detectable level could be 
further enhanced by taking a larger air sample. 

Similar experiments with an RDX and a TNT 
bomb were unsuccessful. Further work is needed 
to determine whether the cartridge would have 
trapped and released these compounds if they had 
been present in the post-blast air. 


A. 


B. 





TIME 

(Minutes) 

GC-TEA 
(x 16) 



TIME 

(Minutes) 

HPLC-TEA 
(X 3 2) 


Figure 5. Chromatograms on GC-TEA and HPLC-TEA of 
an extract from post-explosion debris of a detonating cord 
bomb. On GC-TEA a 0.2 ul injection of debris extract showed 
NG, and a trace of EGDN. On HPLC-TEA, a 5 ul injection 
indicated NG, and a trace of PETN. 


peak shape of PETN, which undergoes partial 
decomposition in the GC. Similarly, for the letter 
bomb, PETN was the only explosive that was de¬ 
tected on the hands. 

Controlled experiments with handswabs that 
had been spiked with known amounts of explo¬ 
sives, indicated a lower detection limit of about 10 
pg injected on column. Again, because of the se¬ 
lectivity of the detector, clean-up was not re¬ 
quired. 


Handswab Experiments 

Figure 8 shows the chromatograms for the gel 
dynamite handswab. Both EGDN and NG are 
seen to be present in relatively large quantities (the 
TEA analyzer was on attenuation x 128 for GC 
and x 256 for HPLC). For the handswab from 
C-4, only a single chromatographic peak due to 
RDX was observed (Figure 9). For plastic explo¬ 
sive, see Figure 10, the handswab extract con¬ 
tained mainly PETN, with only a trace of NG. 
The GC-TEA chromatogram shows the typical 


CONCLUSION 

The capability for routine detection of explo¬ 
sives at the low picogram level from ‘real world’ 
samples of military explosives, post-explosion 
debris, and handswabs, has been demonstrated. 
Because of the selectivity of the TEA analyzer, 
clean-up is not needed. The analytical methods 
are, therefore, simple and rapid. The minimum 
detectable amount for most explosives in 4-5 pg 
injected on column. 


173 

































DETECTOR RESPONSE (ARBITRARY UNITS) 


A. Standards: B. Sample 

(T) EGDN 



TIME TIME 

(Minutes) CMinutes) 

Figure 6. Chromatograms on H PLC-TEA ( x 16) of 5 explosive standards (Figure 6A) and a 20 ul injection of the extract from post 
explosion debris of a C4 bomb (Figure 6B). The peak identification is 1-EGDN, 2-TNT, 3-NG, 4-PETN and 5-RDX. The 20 ul 
injection of debris extract contained 5 ng of NG, 6.8 ng of PETN and 9 ng of RDX. 


174 



































Figure 7. Chromatograms on HPLC-UV-TEA of an air 
sample which had been collected on a Thermosorb/N Car¬ 
tridge, following a blast from a dynamite bomb. The 20 ul in¬ 
jection indicated the presence of 9 ng of EGDN. 


175 

















© ® 




TIME 

(Minutes) 


TIME 

(Minutes) 


CC-TEA 
(x 1 28) 


HPLC-TEA 
AHn x256 


Figure 8. Chromatograms on GC-TEA and HPLC-UV-TEA of a gel dynamite handswab extract. The injection volume was 0.2 ul 
on GC-TEA ( x 128) and 1 ul on HPLC-TEA ( x 256). Peak 1 coeluted with EGDN, and peak 2 with NG. 


176 





























J_I_I_L 

0 5 10 15 


HPLC-UV 



TIME 

(Minutes) 


TIME 

(Minutes) 


GC-TEA HPLC-TEA 

(x64) (x256) 


Figure 9. Chromatograms on GC-TEA and HPLC-UV-TEA of a C4 handswab extract. The injection volume was 0.3 ul on 
GC-TEA ( X 64) and 20 ul on HPLC-TEA ( X 256). Only a single major peak, due to RDX, was observed on both GC and HPLC. 


177 



























A 


HPLC-UV 

254 nm, 0.01 AuFS 



TIME 

(Minutes) 


TIME 

(Minutes) 


GC-TEA 
(x 16) 


HPLC-TEA 
(x 128) 


Figure 10. Chromatograms on GC-TEA and EIPLC-UV-TEA of a handswab from a person who had handled a plastic explosive. 
On GC-TEA 0.4 ul of the 2 ml extract was injected. A trace of NG (0.21 ng) and PETN was shown to be present (note the typical 
peak shape of PETN which decomposes on the column). For HPLC-TEA ( x 128), 3 ul was injected, giving a PETN peak due to 84 
ng. 


178 






















ACKNOWLEDGEMENTS 

We are grateful to Dennis Reutter and Ed 
Bender of the FBI for collecting the post-blast 
debris samples of the TNT, C-4 and detonating 
cord bombs, and the post-blast air sample. 

We thank Steven Prescott of Air Products and 
J. M. F. Douse of the Metropolitan Police, 
United Kingdom for making a copy of their manu¬ 
scripts available to us prior to publication. We 
thank James Buckley and David Rounbehler for 
many valuable discussions. 

REFERENCES 

Douse, J. M. F. (1982). Trace analysis of explo¬ 
sives in handswab extracts using Amberlite 
XAD-7 porous polymer beads, silica capillary 
column gas chromatography with electron-cap¬ 
ture detection and thin layer chromatography. 
J. Chromatogr., 234: 415-425. 

Douse, J. M. F. (1983). Trace analysis of explo¬ 
sives at the low picogram level using silica capil¬ 
lary column gas chromatography with thermal 
energy analyzer detection. J. Chromatogr., 
256: 359-362. 

Goff, E. U., Yu, W. C., and Fine, D. H. (1983). 
Description of a nitro/nitroso specific detector 
for the trace analysis of explosives. Proceedings 
Int. Symp. on Analysis and Detection of Explo¬ 
sives, Quantico, Virginia. 

LaFleur, A. L. and Morriseau, B. (1980). Identi¬ 
fication of explosives at trace levels by high-per¬ 
formance liquid chromatography with a nitro- 
syl specific detector. Anal. Chem. 


53: 1313-1318. 

LaFleur, A. L. and Mills, K. M. (1981). Trace 
level determination of selected nitroaromatic 
compounds by gas chromatography with pyro¬ 
lysis/chemiluminescent detection. Anal. Chem. 
53: 1202-1205. 

Maddock, J., Lewis, P. A., Woodward, A., Mas¬ 
sey, P. R., and Kennedy, S. (1983). Determina¬ 
tion of Isosorbide Dinitrate and its Mononitrate 
Metabolites in Human Plasma by High-Per¬ 
formance Liquid Chromatography—Thermal 
Energy Analysis. J. Chromatogr. 
273: 129-136. 

Phillips, J. H., Coraor, R. J., and Prescott, S. R. 
(1983). Determination of nitroaromatics in bio¬ 
sludges using a gas chromatograph—thermal 
energy analyzer. Anal. Chem. 55: 889-892. 

Rounbehler, D. P., Reisch, J., Coombs, J., and 
Fine, D. H. (1980). Nitrosamine air sampling 
sorbents compared for quantitative collection 
and artifact formation. Anal. Chem. 52: 273- 
276. 

Twibell, J. D., Home, J. M., Smalldon, K. W., 
and Higgs, D. G. (1982). Transfer of nitrogly¬ 
cerine to hands during contact with commercial 
explosives. J. Forensic Sci. 27: 792-800. 

Yu, W. C., and Goff, E. U. (1983). Determina¬ 
tion of vasodilators and their metabolites in 
plasma by liquid chromatography with a nitro- 
syl-specific detector. Anal. Chem. 55: 29-32. 

Yu, W. C., and Goff, E. U. (1983). Measurement 
of plasma concentrations of vasodilators and 
metabolites by the TEA analyzer. Biopharm. 
Drug Disp. 4, 311-319. 


179 











































































































X-RAY PHOTOELECTRON SPECTROSCOPIC (XPS) DETECTION 
AND IDENTIFICATION OF EXPLOSIVES RESIDUES 


J. Sharma 

Naval Surface Weapons Center 
White Oak 

Silver Spring, Maryland 20910 


ABSTRACT. X-ray Photoelectron Spectroscopy (XPS) is a sensitive and power¬ 
ful analytical technique with which residues in the nanogram range over an area of 
a square centimeter can be detected and identified. The Is spectrum of nitrogen is 
particularly useful because the chemical shift of the nitrogen line distinguishes be¬ 
tween the nitrate ester, nitro, nitroso and amine groups. The relative ratios of these 
groups in the debris can be determined and the explosive identified by the mode of 
molecular fragmentation. Combined with thin layer chromatography, XPS has 
proved to be a highly successful technique for forensic and malfunction investiga¬ 
tions. Examples of specific applications are given. 


INTRODUCTION 

X-ray Photoelectron Spectroscopy (XPS), also 
known as Electron Spectroscopy for Chemical 
Analysis (ESCA) is now a well-established labora¬ 
tory technique. It measures the binding energy of 
the electronic levels in a given sample. (Siegbahn 
et al. (1967), Brundle and Baker (1977)). The en¬ 
tire range of occupied electronic levels below 1500 
eV binding energy is accessible to the XPS tech¬ 
nique, giving it powerful analytical and research 
capabilities. Since the electronic level structure of 
any material is a reflection of its physical and 
chemical state, XPS has unravelled many metal, 
alloy, insulator, semiconductor, and catalyst 
problems. The technique has played a major role 
in surface physics due to its high sensitivity to the 
top surface layers of a solid. 

In the field of explosives, the technique has been 
applied to study the electronic levels of primary 
and secondary explosives and the ingredients of 
rocket and gun propellants. This research has elu¬ 
cidated the different modes of molecular frag¬ 
mentation caused in explosives by various stimuli 
such as shock, heat, and radiation. (Owens and 
Sharma (1979), Sharma et al. (1982)). As a 
by-product of this study, characteristic XPS 
spectra of explosives have been produced which 
can be used to identify explosives in forensic in¬ 
vestigations of explosives residues. This paper will 
describe some applications of the XPS technique 


to the detection and identification of explosives 
from the debris collected after an explosion. Some 
of the distinct advantages of the XPS technique 
will be pointed out. 

THE XPS TECHNIQUE 

For XPS study, the specimen (typically 5 mm x 
10 mm area) is irradiated with characteristic X-ray 
emmision from a Mg anode (1253.6 eV) or Al 
anode (1486.6 ev) in a vacuum chamber. The 
ejected photoelectrons are energy analyzed in an 
electrostatic or electromagnetic analyser. From 
Einstein’s photoelectric equation we have 
hv = Vi mv 2 + E b 

The binding energy, E b of the electronic level from 
which an electron is ejected, is determined from 
the known photon energy hv and the measured the 
kinetic energy (Zi mV 2 ). The data are usually 
plotted as the number of photoelectrons emitted 
as a function of binding energy. A full XPS spec¬ 
trum displays peaks at all of the occupied elec¬ 
tronic levels of the sample up to the energy of the 
exciting Mg or Al X-rays. 

a. Elemental Identification 

Since all atoms possess a relatively small num¬ 
ber of electronic levels (compared to the thou¬ 
sands of lines in optical spectra), the measurement 
of the core levels leads to a straightforward and 
unequivocal identification of the elements in a 


181 


CLLCTKON 


W'LCTKOMCTLK 



Figure 1. Schematic representation of the XPS measurement. 


given sample. The core levels are also well-sepa¬ 
rated in relation to the resolving power of the in¬ 
strument (1 eV). For example, the Is levels of 
carbon, nitrogen and oxygen, three neighbors in 
the periodic table, are at approximately 285, 400 
and 531 eV respectively. In the rare event of two 
lines from different atoms superimposing, one can 
verify easily by referring to other electronic levels 
of the atoms concerned. The atoms of higher 
atomic number have many electronic levels to 
mitigate this problem. A broad spectral scan from 
0-1000 eV binding energy gives a full elemental 
analysis of the sample and the peak heights indi¬ 
cate the relative ratio of atoms in the specimen. Of 
course, one has to take into consideration the 
photoelectric cross-section of the different levels 
of the atoms. These are available from standard 
tables. The cross-sections over the periodic table 
vary only over a small range, (0.1-30) so that a 
wide scan provides us with a direct picture of rela¬ 
tive concentrations. However, due to problems 
arising out of surface sensitivity of the technique, 
quantitative analysis is restricted to an accuracy of 
about ten percent. 

b. Chemical Shift 

The exact position of an XPS peak depends 
upon the oxidation state of the atom. Oxidation or 
partial loss of outer electrons moves the peaks to 
higher binding energy due to the effect of screen¬ 
ing on core levels by the outer electronic orbitals. 
This chemical shift is often of the order of 10 eV 
and provides us with a powerful handle in the 
identification of explosives. For example, RDX 
and HMX give a pair of peaks, shown in Figure 2, 
at a characteristic separation of 5.7 eV, due to the 
different oxidation states of the amine and nitro 
nitrogen. The relative heights of the peaks are 
indicative of the ratio of the amine and nitro nitro¬ 
gen in the molecule. RDX and HMX both show 
equal peaks because both of them have an equal 
number of nitro and amine nitrogens. When 



Figure 2. The N Is spectrum of F1MX and its post detonation 
residue, showing characteristics separation of 5.7 eV between 
the nitro ~ 406 eV, and the amine ~ 400 eV peaks. 

explosives are degraded by radiation or heat, the 
changes in the molecules are also reflected by the 
nitrogen spectra. 

The nitrogen of nitrate ester shows a maximum 
binding energy of 407 eV, the nitro appears at 
about 405 eV while the nitroso appears at about 
402 eV. The amine nitrogen in most of the explo¬ 
sives is found to be at about 400 eV. This general 
pattern facilitates identification of explosives and 
their classes. Thus, XPS not only identifies the 
atoms in a given sample but it also gives informa¬ 
tion about the chemical environment of the atom. 
For determining the latter, a 20 - 30 eV wide scan 
is made in the region of the Is electronic level of 
nitrogen. 

c. Sensitivity of XPS 

The kinetic energy of the photoelectrons on 
which the measurement of XPS is based is limited 
by the excitation energy (1253.6 or 1486.6 eV). 
Only electrons originating near the surface of the 
sample are capable of emerging and reaching the 
analyzer at these energies. Thus, the sampling 
depth of XPS is about 30 A (six molecular layers)* 
for organic materials while it is about half of that 
value or 15 A for metals. This makes XPS very 
much a surface technique and sometimes the sur¬ 
face can be complicated and different from the 
bulk. On the other hand, since the whole signal is 


182 














originating in the top 30 A of the sample, one can 
get full information from an infinitesimally small 
sample, provided it is well spread on the surface. 
Only 10 s gm. of a given sample is required for 
XPS studies. This feature makes the technique ex¬ 
tremely sensitive. Detection of parts per billion 
from solutions have been reported by Brinen and 
McClure (1972) and even smaller levels have occa¬ 
sionally been detected. Brundle and Roberts 
(1972) have reported surface sensitivity of 2 x 
10 3 atomic or molecular layer. In this respect 
XPS is one of the few techniques ideally suited for 
forensic detection and identification of explosives. 

In the study of explosives by XPS the fact that 
nitrogen is a common constituent gives an advan¬ 
tage because this atom displays an appreciable 
chemical shift. The other advantage with nitrogen 
is that atmospheric nitrogen is inert and will not 
stick to surfaces as a contaminant. By contrast, 
oxygen and hydrocarbon are present on all sur¬ 
faces as atmospheric adventitious impurities 
which can interfere with the interpretation of oxy¬ 
gen and carbon spectra of the sample. No such 
problem is posed by nitrogen. 

CHARACTERISTIC EXPLOSIVES SPECTRA 

Figure 3 shows the spectrum of lead azide; the 
nitrogen Is and 4d levels of lead are exhibited. The 
azides show two nitrogen lines with a characteris¬ 
tic separation of 4.5 eV and in the ratio of 1:2 due 
to the positive and negative nitrogens in the azide 
ion NNN. The lower spectrum is that of lead azide 
partially decomposed by UV photolysis. Figure 4 
shows the spectra of TNT (consisting of a single 
nitro peak), the spectrum of decomposed TNT 
and also the spectrum of explosion residue from 
TNT. The peak at 400 eV is due to the nitroso de¬ 
rivative of TNT invariably produced when TNT is 
decomposed in the solid, liquid or vapor phase, 
either by heat or by radiation. Figure 2 (lower 
curve) is the spectrum of explosion debris of HMX 
from a witness plate. Its similarity to the HMX 
(upper curve) spectrum is obvious. Unfortunately, 
due to the structural similarity between RDX and 
HMX, the XPS technique cannot distinguish be¬ 
tween these two explosives. Figure 5 shows the N 
Is spectra of (a) RDX control, (b) photolysed 
RDX, (c) thermally decomposed RDX and (d) ex¬ 
plosion debris of RDX. The last spectrum shows a 
considerable amount of broadening to the higher 
binding energy side due to the generation of highly 
oxidized gaseous products sticking to the witness 
plate. Photolysis is found to cause a preferential 



Figure 3. The N Is spectrum of lead azide showing two lines of 
nitrogen in the ratio of 1:2 for the N+ andN- in the azide ion. 
The lower spectrum is that of partially decomposed lead azide. 
The peaks at 415 and 436 eV are due to the d levels of lead. 

decrease of the nitro line due to the separation of 
the nitro groups, while the amine group is not 
much affected. It appears (Figure 5 (c)) that ther¬ 
mal decomposition disrupts the whole molecule. 

In the nitrate ester based explosives, such as 
PETN, NG and NC, the nitrogen peak shows up 



Figure 4. The N Is spectrum of TNT, thermally decomposed 
TNT and post detonation residue of TNT. 


183 












Figure 5. The N Is spectrum of (a) RDX control, (b) photo- 
lysed RDX, (c) thermally decomposed RDX and (d) of explo¬ 
sion residue from RDX. 

at 407 eV representing the highest oxidation state 
of the nitrogen. Figure 6 gives the N Is spectrum 
of PETN along with that of its explosion residue. 
PETN shows some peaks in the nitro region when 
it is decomposed. This is evident in the above spec¬ 
trum. 

All of the spectra mentioned in this paper show 
that the Is nitrogen spectra of residues in the range 
of 410-395 eV can help in the detection and iden¬ 
tification of explosives. Even in the case of a high 
order detonation, at least a fractional percent of 
the original explosive will be scattered without full 
destruction, and can stick to the surrounding area. 
Consequently, if swabs and debris are collected 
from the area of an explosion, XPS analysis com¬ 
bined with other techniques can lead to a success¬ 
ful investigation. XPS has also been used in many 
successful investigations of weapons malfunction, 
where it played an especially critical role in distin¬ 
guishing between the areas exposed to explosives 
and ones exposed to propellants. 

A few concrete cases of investigations in which 
XPS has been of critical help are mentioned in the 
following. 

CASE STUDIES 

A number of empty, new steel shells were being 
heat treated for improving their fragmentation 



410 405 400 


BINDING ENERGY-ELECTRON VOLTS 

Figure 6. The N Is spectrum of PETN, showing peak at 407 
eV, and that of its explosion debris showing broadening 
towards higher binding energy due to deposition of nitrogen 
oxides vapors on the witness plate. Some nitro products also 
show up at 405 eV. 

pattern. One of them exploded during heating 
causing serious damage to the furnace and the la¬ 
boratory. Only XPS study of the inside wall of the 
exploded shell showed evidence of TNT and its 
thermally produced products. Subsequent tests by 
conventional methods on samples collected from 
the same lot of shells confirmed the presence of 
TNT. It turned out that the vendor had supplied 
used shells which had been cleaned with steam. 
Obviously some shells had escaped a thorough 
cleaning and had caused the explosion. 

A fatal explosion was being investigated. In the 
area of the explosion, a large amount of fertilizer 
consisting of ammonium phosphate and sulfate 
was blown up which made analysis of the residue 
extremely difficult. Only XPS study, Figure 7, 
showed separate peaks due to the ammonium and 
the nitrate ester nitrogen leading to the identifica¬ 
tion of nitroglycerine. In this study, the investiga¬ 
tion was successful because XPS could detect the 
two kinds of nitrogen in the strong background of 
the fertilizer. Once it was known that a nitrate 
based explosive was involved, TLC and mass spec¬ 
trometry confirmed NG. 

In still another investigation, an explosion had 
taken place in lockers, located under automatic 


184 







PHOTO-ELECTRON CURRENT-COUNTS/SEC 



BINDING ENERGY-ELECTRON VOLTS 


Figure 7. The upper curve is the N Is spectrum of NG on TLC 
powder obtained at -70° C. The lower spectrum is that of 
post-detonation residue, showing NG peak at 407 eV distinct 
from that of N in ammonium sulfate or ammonium phosphate. 

sprinklers. The explosion caused the sprinklers to 
operate, and the site was under two inches of 
water, before an investigator could arrive. All the 
evidence of the explosives had been washed away 
and conventional methods of investigation failed 
to give any clue. XPS examination of the de¬ 
formed locker surfaces and their scrapings identi¬ 
fied standard dynamite to be the explosive used. 
Of course, once the clue had been given by XPS, it 
was possible to confirm the finding by TLC and 
mass spectrometry. In such investigations, one 
looks for the spectra of both the explosive and its 


decomposition products. 

In summary, XPS in an analytical technique 
which, along with other methods of analysis, can 
be exceedingly helpful in forensic investigations. 

The author would like to thank his former col¬ 
leagues Drs. W. Fisco, C. Ribaudo, S. Bulusu and 
T. Castorina at ARRADCOM, Energetic Materi¬ 
als Division, Dover, New Jersey 07801, for their 
participation in the investigations and for many 
helpful discussions. 

REFERENCES 

1. Brinden, J. S. and McClure, J. E., (1972). 
Anal. Letters, 5:737. 

2. Brundle, C. R. and Baker, A. D. (1977). Elec¬ 
tron spectroscopy: theory, techniques and ap¬ 
plications, Academy Press, New York, Vol. I. 

3. Brundle, C. R. and Roberts, M. W. (1972). 
Proc. Roy. Soc. Lond. A33L383. 

4. Owens, F. J. and Sharma, J. (1979). X-ray 
photoelectron spectroscopy and paramagnetic 
resonance evidence for shock induced intra¬ 
molecular bond breaking in some energetic 
solids. J. Appld. Phys. 51 (3): 1494—1497. 

5. Sharma, J., Garrett, W. L., Owens, F. J. and 
Vogel, V. L. (1982). X-ray photoelectron study 
of electronic structure and ultraviolet and iso¬ 
thermal decomposition of 1,3,5-tramino- 
2,4,6-trinitrobenzene. J. Phys. Chem. 
86,1657-1661. 

6. Siegbahn, K., Nordling, C., Fa hi man, A., 
Nordberg, R., Hamrin, K., Hedman, J., 
Johansson, G., Bergmark, T., Karlsson, S. E., 
Lindgren, I., Ling berg, B. (1967). ESC A: 
atomic, molecular and solid state structure stud¬ 
ied by mean of electron spectroscopy. Almquist 
and Wicksells: Stockholm. 


185 





















































CHARACTERIZATION AND IDENTIFICATION OF WATER SOLUBLE 

EXPLOSIVES 


John H. Kilbourn 
Criminalist 

State of Alabama Department of Forensic Sciences 
P. O. Box 128, Huntsville, AL 35804 

Thomas J. Hopen 
Criminalist 

State of Alabama Department of Forensic Sciences 
P. O. Box 2344, Montgomery, AL 36103 


ABSTRACT. This paper describes a simple technique whereby water soluble in¬ 
organic explosive compounds are characterized by their crystal shape, size, and 
interfacial angles as they recrystallize from a drop of water on a microscope slide. 
Once the crystals are characterized, the inorganic explosive compound(s) can be 
confirmed by other optical properties and such as refractive indices, extinction 
angles, and birefringence, and/or by conducting microchemical tests. The ad¬ 
vantage of this procedure is that it is fast, inexpensive, only a minute amount of 
sample is needed, and does not require a broad knowledge of optical crystallo¬ 
graphy. A discussion of the characteristic crystals and the identification of the 
common inorganic explosive compounds will be presented. The application of the 
technique to cases received in the laboratory will be demonstrated. 


INTRODUCTION 

Forensic laboratories are often faced with the 
task of analyzing and identifying explosive com¬ 
positions. This type of evidence may be submitted 
as intact mixtures or as residue collected at a 
bombing scene. Usually the analysis involves iden¬ 
tifying the explosive component which may in¬ 
clude one or more of the water soluble inorganic 
compounds (oxidizers) that are present in black 
powders, pyrotechnic mixtures, and in some high 
explosives. 

There are published methods for the systematic 
analysis and instrumental identification of the 
inorganic explosives of these explosives. The main 
disadvantages to these techniques are that they 
normally require large samples, specialized instru¬ 
mentation, are time-consuming, and may only 
give an indication as to the inorganic oxidizer 
present. 

A method for identifying high explosives by 
looking at profile angles and correlating this data 
with other crystal properties has been described by 
McCrone. (7). This paper described a similar ap¬ 
proach to the identification of the water soluble 


inorganic explosives. As with the identification of 
the high explosives, this method has the advan¬ 
tages of speed, simplicity, small sample size (nor¬ 
mally less than 1 mg.) and is inexpensive. 

Characteristic crystal forms are described for 
each of the ten explosives along with other crystal 
data to aid in quick identification. Crystal descrip¬ 
tions that are in italics are considered by the au¬ 
thors to be somewhat peculiar to that compound. 
Photomicrographs and diagrams have been in¬ 
cluded to aid in a better understanding of the de¬ 
scription of the crystals. All photomicrographs 
were taken at the same magnification (lOOx), with 
polarized light, as the compounds recrystallized 
from a drop of water. Therefore, the photomicro¬ 
graphs are indicative of the relative relief and crys¬ 
tal size that should be observed. 

PROCEDURE 

The particles to be studied can best be isolated 
by physical removal with fine forceps or needles 
under the stereo-binocular microscope. Water ex¬ 
traction may be used but could lead to metathet- 
ical reactions if several compounds are present. 


187 


These techniques have already been well covered 
by previous works to which one should refer for 
further information. (1,4,5,8,14,17). 

If the particle is physically removed, the follow¬ 
ing procedure is followed: 

1. By means of a glass rod that has been drawn 
out to one end to a 1 mm tip, place a small drop of 
distilled water 5mm to 7mm in diameter in the cen¬ 
ter of a clean microscope slide. 

2. Add the particle to be investigated into the 
droplet. For all but the very soluble ammonium 
nitrate, the size particle need not be any larger 
than the hole in the letter “b.” 

3. Crush the crystal in the drop with the 
drawn-out glass tip being careful not to spread the 
drop. It is very important to observe only crystals 
that grow entirely submerged; dry crystals are 
badly misformed and much less characteristic. 
Continue crushing the crystals to reduce their size 
and to stir the drop thus aiding dissolution. 

4. Any crust that develops at the edge of the 
drop should be pushed into the center being care¬ 
ful not to spread the drop. 

5. Continue as above until well-formed crystals 
in the drop begin to grow. 

If a water extract has been conducted (on the 
evidence under investigation), the extract should 
be evaporated to a small volume and a drop of the 
extract transferred to a microscope slide. Proceed 
with Step 4 as described above. Successive drop¬ 
lets may be evaporated on the same spot to in¬ 
crease the amounts of solute. This will ensure 
well-formed crystals before the droplet goes dry. 

Once the crystals are characterized, one can 
confirm the identity of the compounds by utilizing 
other crystal properties (i.e. refractive index, melt¬ 
ing points, interference figures, etc.), and/or by 
conducting microchemical tests. This can easily be 
done by redissolving the droplet and splitting it in¬ 
to several fractions or by physically removing the 
crystals from the dried residue. Microchemical 
tests and optical data are listed in the attached Ap¬ 
pendices. 

CHARACTERIZATION 
Nitrate Compounds: 

Barium Nitrate [Ba(N0 3 ) 2 ]. This compound is 
only slightly soluble in water and crystals form at 
the edge of the droplet almost immediately. These 
should be pushed back into the center of the drop. 
Cubes, well formed octahedra, and recognizable 
combinations and distortions thereof soon ap¬ 
pear. Crystals having 60° angles lie on octahedral 


faces; those on cube faces show 120° angles. These 
crystals are isotropic and show moderate relief in 
water. (Figure 1). 

Potassium Nitrate [KN0 3 ]. At first, as the 
droplet evaporates, crystals consisting mainly of 
ill-formed rhombs and chevrons of “L’s” form at 
the very edge, break away, float out to the center 
of the drop, and redissolve. As the droplet nears 
dryness, the crystals consist of well-formed and 
ill-formed rhombs, distorted bipyramids, prisms, 
blades, and rods. These crystals have high retarda¬ 
tion colors. The prisms and rhombs are usually so 
ill-formed that accurate interfacial angles are dif¬ 
ficult to measure. However, the acute angle of the 
rhombs is 77°, the obtuse angle is 103°. The 
prisms have angles of 80° and 140°. (Figure 2). 

Ammonium Nitrate [NH 4 N0 3 ]. This com¬ 
pound is very soluble; additional sample and a 
smaller original droplet will help recrystalization. 
With care, it is possible to obtain thin rods, 
blades, ill-formed prisms, tablets and bipyramids. 
Very gentle warming may help (35-45° C). These 
crystals have high to very high retardation colors, 
depending on the crystal thickness. Ammonium 
nitrate is very deliquescent and if high humidity 
conditions exist, will pick up moisture and redis¬ 
solve. (Figure 3). 

Sodium Nitrate [NaN0 3 ]. Sodium nitrate is 
also very soluble though not as soluble as 
NH 4 N0 3 . Enough solute should be added to satu¬ 
rate the drop before it gets too small and flat. The 
drop almost completely evaporates before any 
crystals appear. A crust may develop which con¬ 
sists of pointed twins and ill-formed rhombs 
which should be pushed back into the drop. 
Numerous well-formed rhombs soon appear and 
a few plates and tablets may develop. These 
rhombs have interfacial angles of 77° and 103°. 
The rhombs have very high retardation colors. 
(Figure 4). 

Lead Nitrate [Pb(N0 3 ) 2 ]. Recrystallizes from 
water as well formed cubes, octahedra, and recog¬ 
nizable combinations and distortions thereof. 
These cubic crystals have very high relief in water. 
(Figure 5). 

All of the compounds of the nitrate group are 
easily identified by their unique crystal forms and 
optical properties. The microchemical tests for 
both the cations and anions are straight forward 
and should not cause any problems. Barium ni¬ 
trate and lead nitrate have similar crystal shapes 
but the difference in their relief in water should 
distinguish the two. 


188 


**-250 um-i 


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Figure 1. Octahedra and cubes of barium nitrate recrystallizing from water. (lOOx) 


Perchlorate Compounds: 

Ammonium Perchlorate [NH 4 C10 4 ]. As the 
drop goes to dryness, two types of crystals de¬ 
velop; a set of two prisms and one or more pina- 
coid views. The latter show 90° angles, the prism 
views are 6-sided and show angles of 135°, 90°, 
135 ° or 117°. It is not necessary to observe all of 
these forms to be sure of the presence of 
NH 4 C10 4 . These crystals are orthorhombic and 
show low retardation colors. (Figure 6). 

Potassium Perchlorate [KC10 4 ]. This com¬ 
pound is slightly soluble and small, well-formed 
crystals immediately appear. These crystals consist 
of equant to rectangular prisms , rhombs , prisms 
(and distortions thereof) and pointed prisms 
where the tip(s) may be truncated. The crystals 
show only low order retardation colors. (Figure 

7). 

Sodium Perchlorate [NaC10 4 .2H 2 0]. Sodium 
perchlorate crystals do not like to form as the 
droplet evaporates unless a little undissolved hy¬ 
drate is left in the droplet. Also, like ammonium 
nitrate, gentle warming may help (35°-40°c). If 
this is the case, you will form diamond shape 


rhombs of the dihydrate. These crystals may be¬ 
come very large in size. The interfacial rhomb an¬ 
gles are 38° and 142°. Low to medium retardation 
colors are observed for these crystals. (Figure 8). 

The perchlorates can easily be identified and 
confirmed by characteristic shapes, optical prop¬ 
erties, and microchemical tests. Even though 
sodium perchlorate may cause some difficulty at 
first, its crystal habits are characteristic and 
should not cause any problems. 

Chlorate Compounds 

Potassium Chlorate [KC10 3 ]. As a drop evapo¬ 
rates, a crust may develop consisting of aggregates 
of partially formed rhombohedra and should be 
pushed back into the drop. Inside the drop 
well-formed platy parallelograms (thin rhombs) 
and small well-formed rhombs develop. These 
have interfacial angles of 80° and 100°, medium 
retardation and symmetrical extinction. (Figure 
9). Also, prisms and octahedra may also develop. 

Sodium Chlorate [NaC10 3 ]. This compound is 
very soluble and the droplet goes to near dryness 
before any crystals develop. However, once re- 


189 


r 





^250 um^ 



Figure 2. (A) Chevrons and rhombs of potassium nitrate recrystallizing from water. (lOOx) (B) Rods and prisms of potassium ni¬ 
trate recrystallizing from water. 


190 




^250 um^ 





Figure 4. Rhombs of sodium nitrate recrystallizing from water. (lOOx) 


191 


£ 




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r> * *' 
o O o 

' ° • o* 

6 * ° ° . * 

e *• € 0 ° 


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o«» 


rf „ o * 

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°0 




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»- 250 um -i O 


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Figure 5. Cubes and octahedra of lead nitrate recrystallizing from water. (lOOx) 



i 


t-250 um H 


4 


Figure 6. Prisms of ammonium perchlorate recrystallizing from water. (lOOx) 


192 


1 






ft 





V ?/ = 



^••“250 um-i 



/ 





Figure 7. Prisms of potassium perchlorate recrystallizing from water. (lOOx) 



I 0 

^250 urn-* 


Figure 8. Diamond shaped rhombs of sodium perchlorate dihydrate recrystallizing from water. (lOOx) 


193 





m > 


K 250 um 


Figure 9. Rhombs of potassium chlorate recrystallizing from water. (lOOx) 





t-250 um-i 


Figure 10. Cubes of sodium chlorate recrystallizing from water. (lOOx) 


194 



crystallization starts, it is spontaneous and the 
droplet is filled with masses of squares , rectangles, 
thin rods, well-formed and distorted octahedra. 
Twinned crystals are common. Sodium chlorate is 
cubic. (Figure 10). 

The characterization of the chlorate compounds 
should not cause any problem. The microchemical 
tests for the cations are considered specific but this 
does not hold true for the chlorate anion since it 
does not form any insoluble crystals. A color 
microchemical test is included in Appendix I but is 
not considered specific for chlorates. 

DISCUSSION 

Sodium nitrate, potassium chlorate, and potas¬ 
sium perchlorate form somewhat similar shapes 
but can easily be distinguished by their respective 
retardation colors (high, moderate, and low re¬ 
spectively). Also, distinguishing lead nitrate from 
barium nitrate is made easy by the fact that lead 
nitrate has a higher refractive index and therefore, 
has higher relief in water. Ammonium nitrate and 
sodium perchlorate may cause some difficulties at 
first, but with a little practice, these are easily 
overcome. Figure 11 lists some characteristic crys¬ 
tal forms and optical data that can be used for 
identification. 

WATER SOLUBLE EXPLOSIVES 

(Under polarized and crossed polarized light) 

Compound 

ISOTROPIC 

Ba(N0 3 ) 2 , n = 1.571, cubes, pointed tablets, octa¬ 
hedra. (Medium relief in H 2 0) 

Pb(N0 3 ) 2 , n = 1.781, cubes, pointed tablets, 
octahedra. (High relief in H 2 0) 

NaC10 3 , n = 1.518, squares, rectangles, square- 
ended prisms. (Twinning is common) 

LOW BIREFRINGENCE 
NH 4 CIO 4 , n’s = 1.482-1.488, well formed prisms 
of two types. 

KCIO 4 , n’s = 1.473-1.477, rectangular prisms, 
rhombs. 

MEDIUM BIREFRINGENCE 
NaC10 4 .2H 2 0, diamond shaped rhombs. (Only 
appear if undissolved crystals of the hydrate is 
present) 

KC10 3 , n’s = 1.415-1.523, well formed rhombs. 

HIGH BIREFRINGENCE 
NaN0 3 ,n’s = 1.336-1.587, well formed rhombs. 
KN0 3 , n’s = 1.335-1.506, rhombs, prisms, chev¬ 
rons (or “L’s”) (usually ill formed). 


NH 4 N0 3 , n’s = 1.413-1.637, rods, blades, ill- 
formed bipyramids. 

The procedure has been performed on cases that 
were submitted to the laboratory for analyses with 
several examples listed below. The procedure used 
to separate the oxidizer include physical removal 
and water extraction. 

Case Example 1: 

Several types of high explosive materials were 
submitted for analyses. These included 
water-gels, extra gelatin dynamites, and straight 
dynamites. The inorganic oxidizer was isolated by 
“particle picking.’’ Ammonium nitrate and 
sodium nitrate were identified in their respective 
dynamites without any difficulty. 

Case Example 2: 

An aluminum powder was submitted to deter¬ 
mine if it were a pyrotechnic mixture. Macro¬ 
scopic examination revealed a fine powder ad¬ 
hered to the surface of the aluminum flakes but 
were too small for particle picking. Crystals from 
a droplet of the water extract were identified as 
sodium nitrate. 

Case Example 3: 

A tan powder was submitted to determine if it 
were an explosive mixture. A water extract was 
conducted and a mixture of potassium chlorate 
and potassium perchlorate was identified. (Also 
quartz and sulfur were identified by other micro¬ 
scopic procedures.) 

Case Example 4: 

A white powder was submitted to determine if it 
was a pyrotechnic compound. Potassium perchlo¬ 
rate, potassium nitrate, and barium nitrate were 
identified utilizing this procedure. (Also, starch, 
diatoms, and strontium nitrate were identified by 
other microscopic techniques.) 

SUMMARY 

This procedure provides a quick, inexpensive, 
and easy method for the identification of inor¬ 
ganic compounds (oxidizers) that may be encount¬ 
ered in high explosives, in flash powders, or as 
residue from a bombing scene. There is no prob¬ 
lem in distinguishing any of the compounds from 
each other, whether in the pure state or in a mix¬ 
ture. Practicing first with knowns, it will save 
hours in analytical time in the long run. Even if in¬ 
strumental methods are used to confirm the iden¬ 
tification, it would still save sample preparation 


195 


and analysis time by not requiring that non-explo¬ 
sive compounds be analyzed. 

ACKNOWLEDGEMENTS 

A special “Thanks” to Dr. W. C. McCrone, 
Dr. Richard A. Roper, Ms. Barbara Blaylock, and 
Mrs. Michelle Sloan for their patience and help in 
preparing this manuscript. 

APPENDIX I 

Microchemical tests provide a very quick and simple means 
of confirming the presence of inorganic ions. For a more com¬ 
prehensive overview of the topic, one should refer to the liter¬ 
ature (11-13). The microchemical tests that are needed to con¬ 
firm the presence of the cations and anions listed in this paper 
are described. 

Sodium (Na + ). 

Dissolve the sample to be tested in a small drop of water. 
Near this drop (but not touching) dissolve a few crystals of zinc 
acetate and uranyl acetate in a drop of water acidified with ace¬ 
tic acid. Draw the reagent drop toward the drop to be tested 
until they meet. Characteristic octahedra will appear if sodium 
is present. 

Potassium (K+). 

Add a drop of chloroplatinic acid near the drop to be tested 
(only a portion of the original sample should be used) and then 
draw the two drops together. High refractive isotropic orange 
octahedra indicate the presence of potassium. Ammonium 
forms isomorphous crystals with chloroplatinic acid and must 
be tested for by the method described below. If the ammonium 
test is negative, then the presence of potassium is confirmed. 

Ammonium (NH 4 + ). 

A hanging drop method is used to test for the ammonium 
ion. Take a drop of the chloroplatinic acid and place it in the 
center of a coverslip. Take the sample to be tested and place it 
on a microscope slide and encircle it with a piece of glass tubing 
(8 mm length, 12 mm I.D.). Add a little dilute NaOH to the 
substance on the microscope slide and cover the glass ring im¬ 
mediately with coverslip (inverted) bearing the chloroplatinic 
acid. Yellow octahedra will appear in the hanging drop of chlo¬ 
roplatinic acid which confirms the presence of ammonium. 
Slight warming of the slide may speed the migration of the am¬ 
monia to the reagent drop. 

Lead (Pb+ +). 

Add a very tiny crystal of potassium iodide to a drop of 
water on a microscope near the very dilute test drop and draw 
the two drops together with the drawn-out glass tip. Bright yel¬ 
low hexagonal plates will form often showing thin-film inter¬ 
ference colors. Excess KI will convert these hexagons to white 
needles. 

Barium (Ba+ +). 

A drop of saturated aqueous squaric acid is placed on a mi¬ 
croscope slide near the test drop (acidified with nitric acid). 
When the drops are allowed to run together, barium forms 
blades and parallelopipeds (singly and in rosettes). 

Nitrate (NO3 -). 

Test No. 1: Dissolve a crystal of nitron in a drop of dilute 
acetic acid on a microscope slide near a drop of unknown sub¬ 
stance. Draw the drops together and at once you will obtain 


sheaves of long, very slender needles and imperfect radiates. 

Test No. 2: Dissolve a crystal of sulfanilic acid and a crystal 
of alpha-naphtylamine in a drop of dilute acetic acid on a 
microscope slide (or white spot plate). Add the test substance 
and a minute amount of zinc dust. A deep red color is pro¬ 
duced. 

Chlorate (CIO3-). 

Place a drop of distilled water on a microscope slide (or 
white spot plate) and acidity with H 2 SO 4 . Add a crystal of ani¬ 
line sulfate and then the substance to be tested. A green¬ 
ish-yellow is produced which goes to blue color. Also, an odor 
of chlorine gas can usually be detected. This test is not consid¬ 
ered specific for chlorates. 

Perchlorate (CI04 - ). 

The substance to be tested is dissolved in a drop of water and 
a few crystals of strychnine sulfate is added. A precipitate of 
simple rectangular and lath crystals will develop. 

APPENDIX II 

Barium Nitrate 

Crystal Class: Cubic 
Refractive Index: n = 1.571 
Melting Point: 592° 

Potassium Nitrate 

Crystal Class: Orthorombic 

Refractive Indices: 0 = 1.335, p = 1.5056,y = 1.5064 
Birefringence: 0.1714 
2V = 7°(~) 

Fusion Data: Inverts at 129° C to rhombohedral phase. 
Melting Point: 333° 

Ammonium Nitrate 

Crystal Class: Orthorombic at 25 0 C 
Refractive Indices: a = 1.413,/) = 1.611, y = 1.637 
Birefringence: 0.224 
2V = 35 0 (-) 

Fusion Data: Converts to biaxial form at 32° C, to tetra¬ 
gonal form at 84° C, and to cubic form at 125° C. 

Melting Point: 155°C. 

Sodium Nitrate 

Crystal Class: Hexagonal 

Refractive Indices: co = 1.5874, e = 1.3361 

Birefringence: 0.2493 (-) 

Melting Point: 308 °C 

Lead Nitrate 

Crystal Class: Cubic 
Refractive Index: n = 1.781 
Melting Point: 470° 

Ammonium Perchlorate 

Crystal System: Orthorombic 

Refractive Indices: a = 1.4818,/) = 1.4833, y = 1.4881 
Birefringence: 0.0063 
2V = 70° (- ) 

Melting Point: Decomposes on heating 

Potassium Perchlorate 

Crystal System: Orthorombic 

Refractive Indices: a = 1.4731, /) = 1.4737, y = 1.4769 
Birefringence: 0.0038 
2V = 50°( + ) 

Melting Point: Decomposes at 400° C 


196 


Sodium Perchlorate 

Crystal System: Orthorombic 

Refractve Indices: a = 1.4606,/?= 1.4617, y = 1.4730 
Birefringence: 0.0124 
Melting Point: Decomposes on heating 
Note: May also exist as hydrate form which belongs to 
monoclinic crystal class. 

Potassium Chlorate 

Crystal System: Monoclinic 

Refractive Indices: a = 1.415,/? = 1.517, y = 1.523 

Birefringence: 0.108 

2 V = 28° (- ) 

Melting Point: 368° 

Sodium Chlorate 

Crystal Class: Cubic 
Refractive Index: n = 1.518 
Melting Point: 248° 

REFERENCES 

1. Beveridge, A. D., Payton, S. F., Audette, 
R. J., Lambertus, A. J., and Shaddick, R. C. 
(1975). Systematic Analyses of Explosive Resi¬ 
dues, Journal of Forensic Sciences, Vol. 20, No. 
3:431-454. 

2. Chamot, E. and Mason, C. (1940). Handbook 
of Chemical Microscopy, Volume II, Second 
Edition, John Wiley and Son. 

3. Hartshorne, N. C. and Stuart, A. (1970). Prac¬ 
tical Optical Crystallography, Second Edition, 
Edward Arnold, London. 

4. Hoffman, C. M. and Byall, E. B. (1974). Iden¬ 
tification of Explosive Residues in Bomb Scene 
Investigations, Journal of Forensic Sciences, 
Vol. 19, No. 1:54-63. 

5. Meyers, R. E. (1978). A Systematic Approach 
to the Forensic Examination of Flash Powders, 
Journal of Forensic Sciences, Vol. 23, No. 
1:66-73. 

6. Midkiff, C. R. and Washington, W. D. (1974). 
Systematic Approach to the Detection of Ex¬ 
plosive Residues. III. Commercial Dynamite, 


JAOAC, Vol. 57, No. 5:1092-1097. 

7. McCrone, W. C. (1959). The Identification of 
High Explosives by Microscopic Fusion 
Methods, Microchem J., Vol. 111:479-490. 

8. McCrone, W. C. and Delly, J. G. (1973). The 
Particle Atlas, Vol. I, Second Edition, Second 
Edition, Ann Arbor Science Publisher. 

9. McCrone, W. C., Delly, J. G., and Palenik, 
S. J. (1979). The Particle Atlas, Volume V, 
Second Edition, Ann Arbor Science Publishers. 

10. McCrone, W. C., Personal Communication. 

11. McCrone, W. C. and Delly, J. G. (1973). The 
Particle Atlas, Vol. II, Second Section Edition, 
Ann Arbor Science Publishers. 

12. Parker, R. G., Stephenson, M. O., McOwen, 
J. M., and Cherolis, J. A. (1975). Analysis of 
Explosives and Explosive Residues. Part 
I: Chemical Tests, Journal of Forensic 
Sciences, Vol. 20, No. 1:133-140. 

13. Prist era, F., Halik, M., Castelli, A., and 
Fredericks, W. (I960). Analysis of Explosives 
Using Infrared Spectroscopy, Analytical Chem¬ 
istry, Vol. 32, No. 4:495-508. 

14. Washington, W. D. and Midkiff, C. R. 
(1972). Systematic Approach to the Detection 
of Explosives. Basic Techniques I, JAOAC, 
Vol. 55, Vol. 4:811-822. 

15. Whitman, V. L. and Wills, Jr., W. F. (1977). 
Extended Use of Squaric Acid as a Reagent in 
Chemical Microscopy, The Microscope, Vol. 
25, No. 1. 

16. Winchell, A. N. and Winched, H. (1964). The 
Microscopical Characters of Artificial Inor¬ 
ganic Solid Substances: Optical Properties of 
Artificial Minerals, Academic Press, New York, 
New York. 

17. Yinon, J. and Zitrin, S. (1981). The Analyses 
of Explosives, First Edition, Pergamon Press. 

18. The Merck Index, Ninth Edition,, Merck and 
Company, Inc., Rahway, New Jersey. 


197 

































































































ION CHROMATOGRAPH OF EXPLOSIVES 
AND EXPLOSIVE RESIDUES 


Dennis J. Reutter, PhD. 
Richard C. Buechele, B.S. 
*Forensic Science Research 
and Training Unit 
FBI Academy 
Quantico, VA 22135 


ABSTRACT. Explosives which contain primarily water soluble ingredients are 
frequently encountered by the forensic scientist. Determining the identity of the 
many slurry explosives now being used in a growing number of bombing cases is 
one area where ion chromatography (IC) has been most useful. There are numer¬ 
ous commercial dynamites and blasting agents sold by approximately a dozen ma¬ 
jor manufacturers which are all comprised primarily of NH 4 N0 3 , KN0 3 and 
NaN0 3 , with varing amounts of water and both ionic and non-ionic additives. If 
the wrapper has been removed from these products before they are incorporated 
into an improvised explosive device (IED), their identification can be a formidable 
task. With the voluntary cooperation of explosive manufacturers, the FBI Labora¬ 
tory is building a collection of commercial products most likely to be used in 
IED’s. In order to analyze these explosives, the Laboratory has developed novel 
procedures for sample preparation and has developed IC procedures for some ions 
which were not previously determined by IC. The extremely high sensitivity and 
selectivity of IC makes the technique extremely valuable for the analysis of 
post-blast residues. Following extraction of the debris with water or a wa¬ 
ter-methanol solution, the extract is simply filtered and run on the IC under condi¬ 
tions identical to those used for the analysis of the undetonated explosive. We have 
shown that this form of analysis offers several advantages over other techniques 
when the ionic residues are volatile or electrochemically active. 


Since its introduction to the FBI Laboratory in 
early 1980, Ion Chromatography (IC) has been 
used to determine ionic materials in many cases. 
One of the most successful applications of IC has 
been in the analysis of explosives. 

Ion Chromatography is a new term for most 
people in the field of explosives analysis. Despite 
several excellent review articles on IC (1, 2, 3) it is 
appropriate to give an elementary introduction to 
the subject before describing the specialized appli¬ 
cations which we have developed. IC is a sub-dis¬ 
cipline of high pressure liquid chromatography 
(HPLC) which is applicable to the determination 
of all ionic material. The instrument itself is essen¬ 
tially an HPLC which uses an analytical column 
packed with a low capacity ion exchange resin. 
The mobile phase (also called eluent) is an 
aqueous buffer solution which may contain some 


organic solvent such as methanol or acetonitrile. 
In the chromatographic process, the ions are parti¬ 
tioned between the ion exchange resin and the 
eluent. Those ions with low pka’s are generally re¬ 
tained least, although ionic size and overall charge 
can also influence retention. The eluent strength is 
determined by the pL, of the salt (s) used to make 
the buffer solution and by the ionic strength of the 
solution. Selectivity is influenced by the pH and 
dielectric constant of the eluent. 

Detection can be accomplished by an HPLC de¬ 
tector which responds to the ions of interest. Con¬ 
ductivity detection is most commonly used be¬ 
cause, by definition, it responds to all ions in 
aqueous solutions. Modern technology allows 
flow-through conductivity cells with advantages 
of simplicity, sensitivity, reproducibility and lin¬ 
earity. The major problem associated with con- 


199 


CATION ANALYSIS 


ANION ANALYSIS 


SAMPLE 

INJECTION 


SEPARATOR 

COLUMN 


SUPPRESSOR 

COLUMN 


CONDUCTIVITY 

CELL 






ELUENT 


X” = F~, Cl ,N0 2 , P0 4 3 ” , Br . N0 3 .S0 4 2- 

Resin—N* HC0 3 ” + Na*X'^ Resm-N*X~ + Na + HC0 3 




Resin—S0 3 "H + + Na + HC0 3 —* Resin— S0 3 Na + + H 2 C0 3 
Resin—S0 3 ”H + + Na + X" —► Resm-S0 3 " Na * + H + X" 


WASTE 


Figure 1. 


ductivity detection is that it responds to both sam¬ 
ple ions and ions in the buffer solution. Reason¬ 
able analysis times require eluents of approxi¬ 
mately 0.01M buffer salt. This is much more con¬ 
centrated than the ppm sample ion concentrations 
which most analysts are interested in determining. 

There are two different instrumental ap¬ 
proaches to overcome the buffer conductivity 
problem. The most popular uses an additional, 
high capacity ion exchange column to remove the 
highly conductive buffer ions before the eluent 
reaches the conductivity detector. Figure 1 illus¬ 
trates how this works for the analysis of anions. 
This technology was invented by Small, Brown, 
and Stevens (1972), then patented and published 
in 1975. The FBI uses instruments of this type. 
The alternative instrumental approach to the buff¬ 
er/conductivity problem does not employ a 
second column. This technique is explained in an¬ 
other paper in this symposium by Dominic Bar- 
sotti. 

The utility of IC for the analysis of explosives is 
obvious when one considers the ingredients used 
in commercial or homemade pyrotechnics, and 
slurry explosives. Perchlorate and nitrate salts are 
the most commonly used oxidizers in domestically 
produced commercial pyrotechnics and home¬ 
made formulations (see Figure 2). Figure 3 shows 
some ingredients used in “water-based” explo¬ 
sives. Ammonium nitrate is the major ionic ingre¬ 
dient in these gels. Other salts such as NaN0 3 , 
KNO3, and Ca(N0 3 ) 2 are used as oxidizers. For 


slurry dynamites, alkylamine nitrates, alkolamine 
nitrates and perchlorate salts are often used as sen¬ 
sitizers. 

Slurry explosives are manufactured by approx¬ 
imately a dozen companies in the United States. 
Each manufacturer offers several formulations, 
each intended for a particular purpose. Correctly 
identifying an unknown slurry by comparing ana¬ 
lytical results to a library of formulations of 
known slurries is a formidable task. To be success¬ 
ful a chemist must have a complete and up-to- 
date collection of known explosives. Further, he 

COMMON INGREDIENTS FOUND IN 
PYROTECHNICS 


OXIDIZERS 

FUELS 

KCI0 4 

Al (powdered) 

nh 4 cio 4 

C (powdered) 

KN0 3 

PVC 

KCIO 3 

Dextrin 

Ba(CI0 3 ) 2 

Sucrose 

Ba(N0 3 ) 2 

Ti (powdered) 

Sr(N0 3 ) 2 

Red Gum 

Sb 4 S e 

Mg (powdered) 
S (powdered) 


Figure 2. 


200 














SOME INGREDIENTS OF 
“WATER-BASED EXPLOSIVES” 


OXIDIZERS 

NH 4 N0 3 

NaNO, 

KN0 3 

Ca(N0 3 ) 2 

Air 


FUELS SENSITIZERS 


Al (powdered) 
Wood Pulp 
Charcoal 
Coal 
Fuel Oil 


Al (powdered) 
CH 3 CH 2 0NH 3 ±N0 3 " 

ch 3 -nh 3 ±no 3 - 

Fuel Oil 
(Picric Acid) 
(Ammonium Picrate) 


Figure 3. 


must be capable of both qualitative and quantita¬ 
tive analysis for the ingredients in each formula¬ 
tion. 

In a forensic laboratory, where one individual 
may be responsible for analyzing all the ingre¬ 
dients in a sample, IC offers significant advan¬ 
tages when compared to some alternative meth¬ 
ods. All ionic materials can, at least in principle, 
be determined by IC. An individual using one in¬ 
strument can do a complete analysis of all ionic 
material in a sample. The sample preparation for 
analysis of explosives by IC is shown in Figure 4. 
This procedure, which involves only homogeniz¬ 
ing, filtering, and diluting is very quick. Sample 
preparation for other types of analysis involve 
lengthy, time consuming steps such as digestion, 
extraction, precipitation, heating, drying, volatili¬ 
zation or derivatization. By eliminating such pro¬ 
cedures, the problems of altering the sample 
through oxidation, reduction, volatilization, in¬ 
complete reactions or poor extractions are com¬ 
pletely eliminating. The major source of quanta- 
tive error for determining ionic ingredient in ex¬ 
plosives by this IC procedure is in obtaining a rep¬ 
resentative sample. 

STEPS IN IC ANALYSIS OF “WATER-BASED 
EXPLOSIVES” AND PYROTECHNICS 


The ion chromatographs in the FBI Laboratory 
are routinely run with more than one detector in 
line (see Figure 5). Whenever possible at least two 
of the detectors are used simultaneously for a sin¬ 
gle chromatographic run. The responses are ra- 
tioed and these ratios are compared with the re¬ 
sults from standards. This practice helps assure 
both the qualitative and quantitative accuracy of 
the results. When sufficient sample is available, 
independent spectroscopic methods are used to 
verify the components in the composition. 

Most of the IC procedures for determining the 
anions in explosives are borrowed from other ap¬ 
plications and used with little or no modification. 
Nitrate can be determined along with F“, CL, 
N0 2 ~, Br~, CIO3 , P0 4 3- , and S0 4 2- in a single 
run using a Na 2 C0 3 /Na 2 HC0 3 eluent. Both con¬ 
ductivity and ultraviolet (UV) absorbance detec¬ 
tors are used in series. The UV detector selectively 
responds to N0 2 ~, Br“, and N0 3 ~ at 210mm. 
This procedure is modified somewhat by a selec¬ 
tive reduction of N0 3 “ to N0 2 " before IC anal¬ 
ysis to allow for the determination of small 
amounts of CICL" in the presence of N 0 3 ~ (see 
Figure 6 ). Perchlorate is determined in a separate 
IC run using an eluent of 0.005 M Nal and a silver 
form halide suppressor column. No anions have 
been found to interfere with C10 4 “, and this meth¬ 
od offers ppm sensitivity (4). 

Methods suitable for the analysis of the mono¬ 
valent cations in explosives had to be developed 
when the published IC procedures proved inade¬ 
quate for explosives analysis (5). Many monova¬ 
lent alkylamines and alkolamines which are or can 
be used as sensitizers in slurries are unresolved 
from alkali metals using aqueous HC1 or HNO 3 
eluents. Figure 7 shows a chromatogram of a solu¬ 
tion containing lOppm each of Na + , NH 4 + , K + , 
and monomethylamine (MMA). There K + and 


Obtain Representative 
0.5 g Sample 


I 


Homogenize in 
250 ml D.l. H,0 


I 


Filter 


I 


Dilute 1/100 


Divalent cations 

Mg 2 *, Ca 2 *, 
Ba 2 *,Sr 2 * 


Monovalent cations 

Na* NH/, MEA*, 
MMA*, K* 


‘Normal Anions’ 
S 2 ‘, N0r, CIO3- 


I 


ICE 

Organics 


Large Anions 

cior 


SYSTEM FOR ANALYSIS OF ANIONS 
IN EXPLOSIVES AND EXPLOSIVE RESIDUES 


Eluent 


Pump 


Injection 

Valve 


Anion 

Separator 

Column 


Anion 
Suppressor 
rh Column 


O— ^“O - 

Electrochemical Conductivity 
Detector Detector 


Variable 
Wavelength 
UV-V is 
Absorbance 
Detector 


—>WASTE 


Figure 4. 


Figure 5. 


201 






















































QUANTITATION OF 1 ppm C\Q 3 - IN 20 ppm N0 3 “ 


1 ppm CI0~ 
20 ppm N0 3 “ 


Reduction 

Cd-Cu 100 mesh catylist 
150 x 3 mm 


qio 3 - 

mN0 3 - 



PH 11.5 

Iml/min. N0 2 “ 

n 

•i 

I I 



P 

0 


CONDITIONS 

Eluent: .030 M NaHCO, 
.024M Na z C0, 

Flow: 3.06 ml/min. 
Separator: 3 x 250 mm 
Anion 

Suppressor: 6 x 50 mm 
Anion 


Conductivity 

Detector Setting: 10 M MH0/8/cm 
= FS 

UV Detector: .310 AUFS = FS 



T 

5 


Conductivity 

UV Absorption 

210 mm 

Time (min.) 
10 ' 


Figure 6. 


MMA appear as one unresolved peak. The addi¬ 
tion of 40 percent methanol to the eluent changes 
the column selectivity (6) and allows for baseline 
resolution of all four cations (Figure 8). Figure 9 
shows the chromatogram of the monovalent ca¬ 
tions in a DuPont Tovex dynamite. The column 

ANALYSIS OF MONAVALENT CATIONS 
IN “WATER-BASED EXPLOSIVES” 


Concentration (ppm) _ CONDITIONS 



selectivities for several alkylamines, alkolamines, 
and alkali metals were determined for eluents con¬ 
taining concentrations of methanol ranging from 
0 to 40 percent (Figures 10 «& 11). 


ANALYSIS OF MONOVALENT CATIONS 
IN “W ATER-BASED EXPLOSIVES” 


CONCENTRATION (ppm) 
Na+ 1 

NH.+ 1 

MMA+ 1 

K+ 1 


_CONDITIONS_ 

Eluent: 0.10 N HCI 

60% H,0/40% Methanol 

Flow: 1.97 ml/min. 


Na + 


Water 


NH + 


MMA+ 



Separator 

Column: 

Suppressor 

Column: 

Injection 

Volume: 


6 x 250 mm cation 
Separator column 

9 x 250 mm cation 
Suppressor column 


100 jjl\ 


Meter Full 

Scale Setting:! >*MH0/cm 


10 


15 


20 


Time (minutes) 


25 


Figure 7. 


Figure 8. 


202 


























ANALYSIS OF MONOVALENT CATIONS 
IN A SAMPLE OF “TOVEX” 


TOVEX 

1 g Tovex/50 I H,0 


_CONDITIONS_ 

Eluent: 0.010 N HCI 

60% H;0/40% Methanol 


Na+ 



Flow: 1.97 ml/min. 

Separator 6 x 250 mm cation 

Column: Separator column 

Suppressor 9 x 250 mm cation 

Column: Suppressor column 

Injection 

Valve: 100*1 

Meter Full 

Scale Setting: 1*MH0/cm 


H J 71 71 71 7 Time (minutes) 

0 5 10 15 20 25 


Figure 9. 

The determination of divalent cations in slurries 
has become more important recently with the in¬ 
creasing use of Ca(N0 3 ) 2 as a partial replacement 
for NH4NO3, NaN0 3 , and KNO3. Calcium ion 
can be determined along with Mg 2+ , Sr 2+ , and 
Ba 2+ in a single IC run using a procedure devel¬ 
oped for a general analysis of soluble alkali earths 
(Figure 12) (7). Diperchlorate or dinitrate salts of 
ethylene-diamine have also been used to sensitize 
slurry explosives. A suitable procedure for ethyl¬ 
ene-diamine determination was developed (8) by 
this laboratory. That procedure has a minimum 
detectable limit of 0.5ppm and is linear between 0 
and 25ppm. A representitive chromatogram is 
shown in Figure 13. 



Figure 10. Relationship between selectivity (a) and percent 
methanol in the mobile phase for monovalent amines. A = 
Ethanolamine, □ = diethanolamine, O = methylamine, ▲ = 
triethanolamine, O = ethylamine, ♦ = triethylamine, • = 
diethylamine, ■ = trimethylamine. 



Figure 11. Relationship between selectivity (a) and percent 
methanol in the mobile phase for inorganic monovalent cat¬ 
ions. A = Na* f O = NH4, □ = K\<> = Rb\ ▲ = Cs\ 


The FBI Laboratory is constantly updating their 
files of commercial explosives. When a new for¬ 
mulation is introduced into the market, the labo¬ 
ratory will examine the explosive to determine if 
the available methods of analysis are adequate to 
distinguish it from other products. If not, a re¬ 
search project will be initiated to develop the 
needed methods. 

EXPLOSIVE RESIDUES 

The primary differences between analyzing ex¬ 
plosives and their post-blast residues are in sample 
preparation and data interpretation. The high sen¬ 
sitivity and non-destructive sample preparation 
offered by IC give it significant advantages over 
other analytical methods used to analyze residues. 

Bomb fragments or debris from the point of ex¬ 
plosion are extracted with cold deionized water. 
Large specimens can be rinsed using a wash bottle 

ANALYSIS OF DIVALENT CATIONS 
IN IREMITE 


1 g/50 I 


Na*; NHA K* 



_CONDITIONS_ 

Eluent: .0025 N HCI 

.0025 N Phenylene- 
diamine • 2HCI 

Flow: 3.07 ml/min. 

Analytical 6 x 250 mm 

Column: Cation Separator 

Suppressor 9 x 250 mm 

Column: Cation Separator 

Injection 

Loop: 100 

Meter Full 

Scale Setting: 30 >iMH0/cm 
Time (minutes) 


Figure 12. 


203 




































.2 

■o 

<v 

c 

o» 



|—i—i—i—i—|—i—i—i—r—|—i—i—i—i—|—i—i—i—i—| 

0 5 10 15 20 

TIME (MIN) 

Figure 13. 

and the extract collected in a plastic or stainless 
steel tray. A minimum volume of water should be 
used. If it is necessary to rinse the debris with 
more than 250ml of water, it is advantageous to 
re-use some of the water already collected in the 
tray to prevent diluting the extract. Smaller speci¬ 
mens are best extracted by placing them in a beak¬ 
er and covering them with a minimal amount of 
water, followed by several minutes of an ultrason¬ 
ic bath. Table 1 shows the solubilities of some salts 
which would be important to an investigation if 
identified in debris. Also listed are solubilities of 
some building materials which cause interference. 
Most oxidizers and ionic sensitizers are very sol¬ 
uble in cold water. The use of warm or hot water 
will most often increase the background levels due 
to increased solubility of interferences. Following 
extraction, the solution is filtered to remove insol¬ 
uble particulates which could plug the valves or 
poison the column. The filtered extract is then in¬ 
jected onto the IC using the same chromatograph¬ 


ic procedures outlined earlier for analysis of ex¬ 
plosives. 

Table 1. SOLUBILITIES OF SOME SALTS USED IN EX¬ 
PLOSIVES AND SOME COMMON INTERFER¬ 
ENCES 


Solubility 

Salt _ (g/100 ml) _ 

Salts Used in Explosives 
NaNOj 73 

NaC10 3 79 

NH 4 NO 3 65 

Ca(N0 3 ) 2 129 

MMA—N0 3 >150 

Common Interferences 
CaS0 4 «2H 2 0 0.24 

CaC0 3 0.0015 

NaCl 35.7 

CaHP0 4 1 

Once the sample has been extracted the solution 
is susceptible to deterioration. Concentrations of 
alkylamines, NH 4 + , N0 2 “, and N0 3 “ have all 
been shown to be significantly diminished in a so¬ 
lution even if refrigerated in a sealed teflon bottle. 
Presumably the ions are metabolized by bacteria 
or undergo electrochemical reactions with other 
ions in the solution. 

DISCUSSION 

The interpretation of analytical results derived 
from the analysis of debris by IC can again be a 
complicated task. Generally, more ions are meas¬ 
ured at a higher sensitivity with IC than with other 
methods. Consequently the examiner cannot rely 
on a database which was collected using other, less 
sensitive techniques to interpret the IC data. In all 
controlled tests conducted by the post-blast FBI, 
all ions found in the original explosive were de¬ 
tected in the residues, provided that the residues 
were extracted and analyzed within 24 hours after 
detonation. The relative concentration of ions 
changed predictably from the relative concentra¬ 
tions in the unconsumed explosive. Those materi¬ 
als with high vapor pressure and those which are 
thermally labile will be found in much lower con¬ 
centrations than alkali metals or halides. Figure 14 
shows the monovalent cations detected in a resi¬ 
due from a Tovex device. Comparing this chro¬ 
matogram with that shown in Figure 9 illustrates 
the point. Another consideration is that explo¬ 
sions are short, high temperature events. Conse¬ 
quently, reaction products which would not be 
thermodynamically predicted under easily obtain- 


204 










able laboratory conditions can be formed. An ex¬ 
ample is the formation of N0 2 in an explosion 
where no form of oxidized nitrogen was incorpo¬ 
rate in the explosive. The N0 2 ~ was most proba¬ 
bly formed from air according to the reaction: 

V 2 N 2 + o 2 = no 2 

The process can become even more complicated 
by the fact that N0 2 " is readily oxidized to N0 3 ~ 
by the dissolved oxygen in water. Thus it is not un¬ 
common to measure trace N0 3 ~ in residues from 
KC10 3 /Sugar devices. Another example is the for¬ 
mation of NH 4 + during the detonation of black 
powder. 


bombing residues. Black powder pipe bombs, 
KC10 3 /sugar pipebombs, and water based explo¬ 
sives were detonated in metal containers, or in 
crates approximately meter deep. Following deto¬ 
nation of each device, samples were collected and 
brought to the laboratory and analyzed within 24 
hours following the schematic illustrated in Figure 
15. The XRD results were not quantitated. The 1C 
results for the same residues were quantitated be¬ 
fore and after the residue was subjected to XRD 
analysis to show the effect of drying the residue to 
a powder. Table 2 shows this effect for a 
KC10 3 /sugar pipe bomb residue. The first IC run 
clearly identifies C10 3 “, CF, and K + along with 


MONOVALENT CATIONS IN THE RESIDUE 
OF A “WATER-BASED EXPLOSIVE” 


Na* 


CONDITIONS 



Figure 14. 

When the FBI Laboratory first began to analyze 
explosive residues by IC, the chromatograms 
showed the presence of ionic material which could 
be relevent to the case, many of which were com¬ 
pletely missed by X-ray powder diffraction 
(XRD) and chemical spot tests. An experiment 
was designed to compare the capabilibities of 
XRD and IC in analyzing the ionic content of 


ESTABLISHED METHOD OF ANALYSIS 
FOR INORGANIC EXPLOSIVE RESIDUES 



Figure 15. 


Table 2. EFFECT OF DRYING KCI0 3 /SUGAR PIPEBOMB RESIDUE FOR ANALYSIS BY X-RAY POWDER 
DIFFRACTION 


Ions 

K + 

C10 3 “ 

ci- 

Na+ 


Original 
Wash by I.C. 

(wt%) 

41.6 

43.0 

14.0 

.4 


X-ray Powder 
Diffraction 

(Crystals 

Identified) 

kci,kcio 3 

kcio 3 

KCI 


Reconstituted 
Powder by I.C. 

(wt%) 

44.3 

28.7 

26.2 

.5 


205 















small amounts of N0 2 ~, N0 3 ~ and Na + . The 
XRD is successful in qualitatively identifying 
KCIO3 and KC1 but did not detect any other mate¬ 
rials. The analysis of the reconstituted powder by 
IC shows that nearly half of the CIO3 had been 
reduced to Cl during the sample preparation and 
XRD analysis. In this test the reduction of ClCb” 
did not prevent XRD from identifying KCIO3 
crystals in the residue. The IC has been used to 
analyze residues in real bombing cases where it de¬ 
tected minute quantities of CIO3 is important 
when found in any concentration, because it has 
no natural sources. Furthermore, CIO3 will not 
be found in the absence of C10 4 if the latter were 
used as the oxidizer because C10 4 is more stable 
toward reduction than C10 3 ~. Since all commer¬ 
cial pyrotechnic devices produced domestically use 
C10 4 “, it is safe to assume that when CICT" is 
found in the absence of C10 4 that the device 
originated from foreign pyrotechnics or was a 
homemade formulation. Conversely, C10 4 is not 
formed as the result detonation of a C10 3 “ oxi¬ 
dized device, consequently the presence of C10 4 
in residue is indicative of a device derived from a 
U.S. made commercial pyrotechnic. 

The tests conducted with the detonation of wa¬ 
ter-based dynamites were even more dramatic in 
demonstrating how sample preparation can ad¬ 
versely affect the results of an analysis. Table 3 
shows a typical result of debris recovered from a 
device made with Tovex dynamite. The first IC 
run was able to easily detect Na + , N0 3 , NH 4 “, 
MMA + and other ions. The analysis by XRD 
showed only NaNC> 3 . The second analysis by IC 
performed on the powder after it was redissolved 
in DI water shows one reason for the discrepancy; 
Ammonium Nitrate is highly volatile. It decom¬ 
poses according to the reaction: NFb-NCT^) 
NH 3 (g) + HNO)( g ) with a Keq = (20ppb) 2 . Mono- 


methylamine nitrate is at least as volatile. Further¬ 
more, MMA-NO 3 is highly hyposcopic which 
opens the possibility that it may not have been in 
crystaline form at the time when the XRD analysis 
was performed. The volatity of the salts is demon¬ 
strated by the fact that 94% of the NH 4 + ion and 
90% of the MMA + ion were lost between the times 
of the first and second IC analysis. It is also inter¬ 
esting to note that most of the N0 2 ~ and CL were 
lost as a result of XRD analysis. Presumably, the 
N0 2 - was oxidized to N0 3 ~, while the CP was 
lost by the volatization of NH 4 C1. 

If these debris has been from a bombing case, 
and the evidence had been properly collected, 
stored and promptly analyzed, the examiner may 
have been able to correctly identify Tovex as the 
explosive in this case to the exclusion of all other 
domestically manufactured dynamites if he had 
used IC. On the other hand, if that same evidence 
were to have been analyzed by XRD, the examiner 
would only have been able to state that the oxi¬ 
dizer was most probably NaNCb which is com¬ 
mon in most water-based dynamites, blasting 
agents and can be easily purchased in pure form 
for the manufacturer of an improvised explosive 
formulation. 

CONCLUSION 

The FBI Laboratory has demonstrated that IC 
can be an important tool for the analysis of pyro¬ 
technics, dynamites, blasting agents and their post 
detonation residues. The techniques have proven 
to be adaptable to the determination of all ionic 
materials currently used in water-based explosive 
and most ionic materials in commercal pyrotech¬ 
nics. The results obtained by this technique have 
proven to both quantitatively and qualitatively re¬ 
liable when performed by scientists who are 


Table 3. EFFECT OF DRYING “WATER-BASED EXPLOSIVE” RESIDUE FOR ANALYSIS BY X-RAY POWDER 
DIFFRACTION 



Original 

X-ray Powder 
Diffraction 

Reconstituted 


Wash byl.C. 

(Crystals 

Powder by I.C. 

Ions 

(wt%) 

Identified) 

(wt%) 

Na+ 

50 

NaN0 3 

64 

no 3 _ 

40 

NaN0 3 

34.2 

nh 4 + 

1.7 


.1 

MMA + 

1.0 


.1 

K + 

.25 


.25 

no 2 _ 

1.0 


.15 

ci- 

4.0 


.3 

so!" 

0.1 


.5 


206 



knowledgeable in the fundamental process under¬ 
lying ion exchange chromatography and ion detec¬ 
tion. Finally, the IC will probably continue to be 
used by the FBI Laboratory to aid in the analysis 
of ionic materials for the foreseeable future. 


REFERENCES 

1. Small, H.; Stevens, T. S.; Bauman, W. C. 
Anal. Chem. 1975 pages 47, 1801-1809. 

2. Small, H. Anal. Chem. 1983 pages 55, 
235-242. 


3. Williams, R. J. Anal. Chem. 1983 pages 55, 
851-854. 

4. Dionex Application Note 18R, Dionex Corp., 
Sunnyvale, CA 3/78. 

5. Dionex Application Note 6, Dionex Corp. Sun¬ 
nyvale, CA 3/78. 

6. Buechele, R. C.; and Reutter, D. J. J. Chrom. 
1982,—. 

7. Dionex Application Note , Dionex Corp, 
Sunnyvale, CA 3/78. 

8. Buechele, R. C.; Reutter, D. J. Anal Chem. 
1982, pages 54,2113-2114. 


207 



































































THE USE OF ION CHROMATOGRAPHY IN 
THE ANALYSIS OF WATER GEL EXPLOSIVES 


D. J. Barsotti, R. M. Hoffman, and R. F. Wenger 

ABSTRACT. This method involves the use of 10% HN0 3 to break down the 
crosslinked network of the water gel. The resulting solution is filtered to remove 
the insoluble components, i.e. glass, perlite, hydrolyzed quar and organic fuel. The 
filtrate is diluted to decrease the individual in concentrations to approximately 100 
ppm. Two sets of chromatographic conditions are necessary for a complete analy¬ 
sis, one set for the monovalent cations Na + , CH 3 NH 3 + , NFI 4 NFL, + , etc. and an¬ 
other for the multivalents such as calcium, etc. Using dual column dual conductiv¬ 
ity detector ion chromatography the concentration is determined using a previously 
determined response factor for each ion of interest. The described method will re¬ 
duce the analysis time from several hours to thirty minutes. The precision (2 p) is 


5% relative. 

INTRODUCTION 

The use of liquid chromatography has been ex¬ 
tended to the analysis of water gel explosives. Tra¬ 
ditional standard methods are both tedious and 
time consuming. These methods are based on 
solubility differences of individual components 
and the reactions of various components with a 
given reagent to form an insoluble precipate or a 
volatile substance. 

These standard methods have been used for the 
past twenty years and although these methods can 
be accurate and reproducible, the analyses are 
time consuming taking approximately 3-5 hours. 
As such, these methods are inappropriate for 
process control when the analyses are for manu¬ 
facturing processes. Therefore, a method was 
needed which is more sensitive and rapid to meet 
requirements for in process control, quality assur¬ 
ance and troubleshooting. The desired analyses 
time is approximately 30 minutes. 

In recent years many techniques have been pro¬ 
posed in literature using chromatography for the 
analyses of explosives. Some of these techniques 
include gas liquid chromatography (1, 2), thin 
layer chromatography (3, 4), and liquid chroma¬ 
tography (5). The technique of ion chromatog¬ 
raphy was developed by Small, et al. (6) in 1975. 
This technique called suppressor-type ion chro¬ 
matography uses the combination of an analytical 
separating column in conjunction with a suppres¬ 
sor column which is used to remove background 
elements in the eluent. A variation to this tech¬ 


nique was proposed by Fritz, et al. (7). This sys¬ 
tem uses a conventional HPLC equipment with 
separating column and a conductivity detector. 
This system (nonsuppressed IC) is readily adopted 
to most liquid chromatographs. 

The nonsuppressed system was used to deter¬ 
mine the inorganic salts, Na + , NH 4 + , CH 3 NH 3 + , 
and Ca + + . This represents approximately 80% of 
the “Tovex” explosives. This analysis time is re¬ 
duced to 25 minutes with a precision of 5% rela¬ 
tive. 

EXPERIMENTAL 

Apparatus 

Ion Chromatograph (IC)—Wescan Model 261 
with dual column and dual detector capability 
equipped with two fixed volume, high pressure in¬ 
jection valves and 100 sample loops. 

Cation columns—Wescan Cat. No. 269-004, 25 
cm x 2.0 mm I.D. with cation guard cartridges, 
Cat. No. 269-005. 

The use of plasticware in place of glassware is 
recommended to prevent sodium contamination 
from the glass. 

Reagents 

All reagents were ACS reagent grade and were 
without further purification except as noted. 

Treated Water—Type I water or distilled water 
passed through a filter train consisting of a combi¬ 
nation deionization/organic removal cartridge 
(Fisher Scientific, Cat. No. 09-035-30), and 


209 


Ultrapure cartridge (Fisher Scientific, Cat. No. 
09-035-25), and a pleated capsule filte. 0.2 um 
pore size (Fisher Scientific, Cat. No. 09-743-50) 
This water is used in all solution preparations: 

Monomethylamine Nitrate (MMAN)—73%. 
Nitric Acid—“Ultrex” grade reagent, J. T. Baker, 

Cat. No. 4801, or equivalently pure nitric acid. The 
trace impurities in lower grades of Nitric Acid will 
contaminate the column causing unstable peak reten¬ 
tion times. 

Column Rinsing Solutions 

0.2m HNO3 —Dilute 1.25 ml Ultrex HNO3 to 
100 ml with water. Transfer to a plastic sample 
bottle and tightly cap. 

RESULTS AND DISCUSSIONS 
Calibration 

Prepare a stock solution by weighing 0.250 g 
NaN0 3 , 0.500 g NH4NO3, 2.00 g Ca(N0 3 ) 2 , and 
0.480 g monomethylamine nitrate into a 100 ml 
plastic volumetric flask. Dissolve in 50 ml of 
treated water and dilute to the mark with treated 
water. Add 10 ml of stock solution to a 1000 ml 
plastic volumetric flask and dilute to the mark 
with treated water. Transfer this calibration solu¬ 
tion to a plastic sample bottle and tightly cap. The 
concentration of NaN0 3 , NH 4 N 0 3 , and 

Ca(N0 3 ) 2 can be calculated from equation (1) and 
the concentration of monomethylamine nitrate 
can be calculated from equation (2). 

Cone; (ppm) = (g weighed;) (100) (1) 

Cone. MMAN(ppm) = (g weighed 
MMAN) (73) (2) 

Monovalent Cations 

In the monovalent cation analysis (NaN0 3 , 
NH 4 N0 3 , MMAN), stabilize one of the IC 
columns and detectors with these condi¬ 
tions: Mobile Phase - 0.0039 M HNO (0.250 ml 
Ultrex HN 03 /liter); Flow Rate - 1.8 ml/min; De¬ 
tector - Range 10. 

The columns are conditioned in the following 
manner; inject the 0.2 M EDTA solution and wait 
for signal to return to baseline, then inject 0.2 M 
HN0 3 solution three times waiting for signal to re¬ 
turn to baseline between injections. 

Inject the calibration solution several times with 
an injection of 0.2 M HN0 3 between calibration 
solution injections. Measure the peak area for 
NaN0 3 , NH 4 N0 3 , and MMAN and calculate a re¬ 
sponse factor (RF) for each compound: 

RF _ (Concj ppm) 

Peak Area, 


Calculate the average RF for each component and 
use that for the sample analysis. The RF’s and 
peak retention times should be determined daily. 

Divalent Ions 

For the calcium analysis, stabilize the other IC 
column and detector with these condi¬ 
tions: Mobile Phase, 1 x 10“ 3 M ethylene diamine, 
pH adjusted to 6.1 with ultrex HN0 3 ; Flow Rate, 
1.5 ml/min; Detector, Range 10. 

The columns are conditioned by injecting the 
0.2 M EDTA solution three times, waiting for the 
signal to return to baseline between injections. 

Inject the calibration solution several times, 
measure the peak are, and calculate a response 
factor (RF) for calcium. 

nr _ Cone. Ca(N 0 3 ) 2 ppm 

KrCa(N0 3 ) 2 — - 

Peak Area C a(No 3)2 

Calculate the average RF and use it for the sample 
analysis. The RF’s and peak retention times 
should be determined daily. 

Sample Analysis 

Weigh 10 grams of explosives in a 250 ml volu¬ 
metric flask. To break down the cross-linked net¬ 
work add 25 ml of 10% nitric acid. The hydrolysis 
time for most “Tovex” products is approximately 
5 minutes. On formulas which contain higher 
levels of aluminum more nitric acid is needed 
along with a longer hydrolysis time. Other acids, 
such as, H 2 S0 4 and HC1 may be used, however, 
caution must be used when HC1 is used in contact 
with stainless steel. The digested sample is diluted 
to 250 ml with treated water. 

For the analysis of monovalent cations pipette 
0.350 ml of sample solution into 100 ml plastic 
volumetric flask and dilute to mark with treated 
water. Running under monovalent cations condi¬ 
tions inject 100 ul of sample and obtain peak areas 
and retention times for Na + , NH 4 + , and 

CH 3 NH 3 + . Figure 1 is a typical scan of mono¬ 
valent cation under the above conditions. 

For the analysis of calcium pipette 3.5 ml of the 
sample solution into a 100 ml plastic volumetric 
flask and add 30 ml of 0.25 M NaOH and dilute to 
mark with treated water. The pH of this solution 
should be between 7-8. Running under divalent 
cation conditions inject 100 ul of sample and ob¬ 
tain peak area for calcium. 

Calculations 

For the monovalent cation analysis: 

% j = (Peak Areaj)(RFj)(7.14) 
(Sample Weight) 


210 





FILE: MADYT.A2S RUN DATE: 

DESIGNATION: M.P.=PH 2.3 

SUBMITTED BY: ION CHROM. LC 
ENTER COMMAND: 


24=JUN-82 TIME: 13:49 


ANALOG CHANNEL: 1 



For the calcium analysis: 

%Ca(NO,) 2 = (Peak Area)(RF)(0.74> 

(Sample Weight) 

Results for various “Tovex” analysis are shown in 


Table 1. This list illustrates the comparison of re¬ 
sults of present technique with those acquired 
using standard methods. Table 1 also indicates the 
precision of the various ions. 


REFERENCES 

1. /. W. F. Davidson, F. J. Di Carlo and E. I. 
Szabo, J. Chromatog. 57 (1971), p. 345-352. 

2. J. C. Hoffsommer and J. M. Rosen. Bull. 
Environ. Contam. Toxic. 7 (1972) p. 177-181. 

3. S. K. Yasuda, J. Chromatog., 51 (1970), p. 
253-260. 

4. F. J. Di Carlo, J. M. Hartigan, Jr., and G. E. 
Phillips. Anal. Chem. 36 (1964), p. 2301-2303. 

5. C. D. McAulely. Symp. Chem. Probl. Con¬ 
nected Stab. Explos. (Proc.) 1979, Vol. 5, 41, p. 
199-218. 

6. H. Small, T. S. Stevens and W. C. Bauman. 
Anal. Chem. 47 (1975), p. 1801. 


Table 1. ION CHROMATOGRAPHIC ANALYSIS RESULTS FOR WATER GEL SAMPLES 





% MMAN 



<Vo AN 



% CN 



% SN 


Sample 

“Tovex” 



Std. 



Std. 



Std.m 



Std. 

Number 

Grade 

Expected Observed 

Dev. 

Expected Observed 

Dev. 

Expected Observed 

Dev. 

Expected Observed 

Dev. 

1 

300 

36.72 

36.12 

0.66 (a) 

30.82 

29.83 

0.79< a) 

— 

— 

— 

13.96 

13.57 

0.25 <a) 

2 

800 

19.99 

20.99 

0.042 - 

42.94 

41.68 

1.29 

— 

— 

— 

8.57 

8.13 

0.21 






14.80 

16.63 

0.33 

17.55 

16.30 

0.42 

9.76 

9.95 

0.11 

3 

SSS 

35.25 

36.87 

1.63 

18.04 

19.37 

0.36 

18.13 

17.99 

0.24 

6.72 

6.80 

0.25 

4 

TR-2 

30.03 

30.96 

2.00 

23.47 

23.99 

1.01< a > 

— 

— 

— 

13.21 

13.44 

0.20* a) 

5 

Extra 

17.28 

19.49 

0.90< a) 











MMAN 

AN 

CN 

SN 


Monomethylamine nitrate 
Ammonium nitrate 
Calcium nitrate 
Sodium nitrate 


The expected values were obtained from the standard analysis. 

The standard deviations (Std. Dev.) were calculated from 3 repeat runs, unless otherwise noted, and reported in absolute percent, 
(a) The standard deviation was calculated from 5 repeat runs. 


Table 1. CONCLUSION 

Ion chromatography can be the basis for a method to control process and quality in the manufacturing of water gel explosives. 
This method is rapid, reproducible and accurate. 


211 











































































THE CHARACTERIZATION OF SOME LOW 
EXPLOSIVE RESIDUES BY ION CHROMATOGRAPHY 

By Terry L. Rudolph 
FBI Laboratory 
Washington, D.C. 20535 


ABSTRACT. A large percentage of improvised explosive devices encountered in 
bombing matters received by the FBI Laboratory involved the use of low explo¬ 
sives such as black powder, potassium chlorate/sugar mixtures and the commercial 
black powder substitute, Pyrodex. The combustion residues of most of these low 
explosives are inorganic in nature and water soluble. Because of this water solubil¬ 
ity they can be analyzed both qualitatively and quantitatively by IC. The character¬ 
ization of several different low explosives by IC is reported. This analysis provides 
a simple and rapid identification for these residues. 


One of the latest analytical techniques to be ap¬ 
plied to explosive analyses is ion chromatography 
(IC). Ion Chromatography is a term coined by the 
Dionex Corporation to encompass all techniques 
used for separating and quantating both inorganic 
and organic ions and in its broadest sense is the 
chromatography of ions. 

The FBI Laboratory has been using IC for two 
years in the analysis of explosives in bombing mat¬ 
ters. Since its very limited use several years ago, 
the FBI Laboratory has greatly increased the use 
of IC until now it is routinely used in many bomb¬ 
ing cases. 

Because of its increased use in both high and 
low explosive bombing matters, but most especial¬ 
ly in low explosive cases, it was decided to formal¬ 
ize a program of study to determine the extent and 
capability of IC in this type of analysis. The initial 
focus of the study was on low explosives. 

It was the object of this study to characterize by 
IC, the pattern of anions and cations of the com¬ 
bustion products or residues of several different 
low explosives. It was felt if each different low ex¬ 
plosive had its own individual IC anion and cation 
pattern or fingerprint, that IC could be used for a 
simple and rapid determination of the low explo¬ 
sives commonly used in improvised explosive de¬ 
vices (IED’s). 

Some of the initial goals were as follows: 

1. Determine if a difference could be seen be¬ 
tween homemade and commercial made 
black powder. 

2. Determine if any ammonium salts were 


formed in black powder residues. 

3. Determine the level of sulfide and thiocynate 
formed in black powder residues. 

4. Determine the anion and cation pattern for 
each low explosive residue examined. 

EXPERIMENTAL AND INSTRUMENTATION 

In the initial experiment four different low ex¬ 
plosives were used, commercial black powder, 
homemade black powder, Pyrodex, a commercial 
black powder substitute and a 50/50 mixture of 
potassium chlorate and sugar. 

The commercial and homemade black powders, 
were composed of potassium nitrate (75%), sulfur 
(10%) and charcoal (15%) while the Pyrodex is 
composed of potassium perchlorate, potassium 
nitrate, sulfur and charcoal. 

Four different tests were conducted in which 
each of the four low explosive mixtures were 
placed in six-inch steel pipes capped at both ends 
and then exploded. The post-blast pipe fragments 
were collected and then washed with approximate¬ 
ly 50ml. of distilled water. A 1 ml. sample of this 
filtered wash was then diluted 1/100 in distilled 
water. This sample was then analyzed by IC. 

The analysis was performed on a Dionex Model 
16 Ion Chromatograph equipped with a 100/^1. 
sample loop and a 6^1. flow through conductivity 
detector. Two other detectors were also used in the 
test, a Dionex Electrochemical Detector with a 
2.6/il. cell and Perkin-Elmer LC-55 variable 
wavelength UV-VISIBLE spectrophotometer with 
a 10/^1. cell. 


213 


| Eluent | 

| Pump I 


— | Recorder | 

Injection 

Port 



Separator 


Column 


Electrochemical 

Cell 


Suppessor 


Conductivity 

Cell 


| Recorder | | Recorder") - 1 UV Cell 1 - ( Waste | 


Figure 1. Block Diagram of Ion Chromatography Set-Up. 


The anion separation was performed with 
Dionex columns i.e. a 3 x 50mm pre-column and a 
4.0 x 250mm separator column in series with a 
Dionex anion fiber suppressor. The mobile phase 
for the anion analysis was 0.003 M 
NaHCOj/0.0024M Na 2 C0 3 at a flow of approxi¬ 
mately 3.0ml./min. 

Cation separation was also performed on 
Dionex cation columns i.e. 3 x 50mm pre-column 
and a 6 x 200mm separator column in series with a 
9 x 150mm. Dionex cation suppressor column. 
The mobile phase was 0.01 N HC1 in 30% ethanol. 

Figure 1 is a block diagram of the IC instrumen¬ 
tation used in this test. 


could experience in bombing matters. The reten¬ 
tion times shown in Figure 2 for the various anions 
were used as a basis of identification for the low 
explosive residue anion patterns. 

Figures 3, 4, 5 and 6 shows the anion patterns 
for the residues of the four explosives used in the 
test. Homemade black powder (Figure 3) shows a 
large quantity of sulfate and a lesser quantity of 
nitrate from unreacted potassium nitrate. There 
also was a slight trace of nitrite ion present. Com¬ 
mercial black powder (Figure 4) has a very similar 
anion pattern to the homemade black powder. 
There is less nitrate in the residue and only a small 
trace of nitrite. This is probably due to the fact 
that commercial black powder usually burns more 
thoroughly and completely than homemade. In 
comparison of several different tests, however, it 
was too difficult to distinguish between home¬ 
made and commercial powders from their anion 
patterns alone. 

Figure 5 shows the anion pattern of Pyrodex’s 
combustion residue. The most prominent feature 
is the presence of chloride in the residue. Chloride 


RESULTS 

Figure 2 is an ion chromatogram showing the 
separation of some of the common anions one 

STANDARD ANIONS 

7 Eluent: 0.003M NaH CO 3 / 

O 0.0024M Na 2 C0 3 



Minutes 

Figure 2. Separation of Common Anions. Peaks: Cl- , 4ppm; 
NO 2 -, 10 ppm; HPO 4 - 2 , 50 ppm; Br~, lOppm; N0 3 -, 
30ppm; SO 4 - 2, 50ppm. 


HOMEMADE 
BLACK POWDER 
RESIDUE 


SO „- 2 



Minutes 

Figure 3. 1C Anion Pattern for Home made Black Powder 
Combustion Residue. 


214 














































COMMERCIAL KCI0 3 /Sugar Residue 

BLACK POWDER 
RESIDUE 

cr 



i—i—i—i—i 

04 8 12 16 

Minutes 

Figuie 4. IC Anion Pattern for Commercial Black Powder 
Combustion Residue. 

PYRODEX 

RESIDUE 



Figure 5. 1C Anion Pattern for Pyrodex Combustion Residue. 



I-1-1-1 

0 4 8 12 


Minutes 

Figure 6. IC Anion Pattern for Potassium Chlorate/Sugar 
Combustion Residue. 

is the main combustion product of perchlorate 
which is present in the Pyrodex. There was also 
present nitrite, nitrate and sulfate to give a very 
characteristic pattern for Pyrodex. Actually the 
peak that is identified nitrate could also be all or 
partly chlorate as chlorate and nitrate elute at the 
same time. This problem will be addressed when 
the UV detector is discussed later. 

Figure 6 is the chromatogram of the anion pat¬ 
tern of the residue from the 50/50 mixture of 
potassium chlorate and sugar. There is a very 
strong chloride peak and a significant amount of 
unreacted chlorate. There can be no question that 
this peak is chlorate because there is no nitrate 
present in the organical explosive mixture. This is 
best shown in Figure 7-a,b which illustrates the 
use of the UV detector in these analyses. 

Figure 7-a shows the common anions that are 
absorbers in the UV at 210nm. Only nitrite, bro¬ 
mide and nitrate absorb, chloride, chlorate and 
sulfate do not. Figure 7-b shows the chlo- 
rate/sugar residue from Figure 6 as detected by 
the UV detector. No peaks are present. 


215 

















ANION ANALYSIS 
UV DETECTOR 



Figure 7. a,b. (a) Separation of Common Anions Using a UV 
Detector, (b) UV Detection of Chlorate/Sugar Residue. 


Figure 8-a,b shows the anion pattern for Pyro- 
dex as detected by the UV detector. Figure 8-a is 
the actual chromatogram showing some organics 
from the Pyrodex that also absorbed along with 
the nitrite and nitrate. As noted previously the ni¬ 
trate peak in the Pyrodex residue could actually be 
a mixture of chlorate and nitrate. Figure 8-b 
shows by the dotted line the height the 

PYRODEX RESIDUE 

CIO, 



Figure 8. a,b. (a) IC Anion Pattern for Pyrodex Residue Using 
UV Detection, (b) Theoretical Limits of Chlorate Ion Which is 
not Detected by the UV Detector. 


NO,- 



Minutes 

Figure 9. IC Anion Pattern for Black Powder Using UV De¬ 
tection. 


nitrate-chlorate peak should be based on a calcu¬ 
lation of the nitrate peak using the conductivity 
detector. Chlorate is evidently formed from the 
perchlorate and constitutes about half of the 
nitrate-chlorate residue. 

The Pyrodex residue differs from the black 
powder residue as detected by the UV detector, be¬ 
cause the black powder residue shows no organic 
peak. Figure 9 shows the anion pattern of black 
powder using the UV detector. Compare Figure 9 
with the black powder anion pattern (homemade) 
from the conductivity detector, Figure 3. 

Using both the conductivity and UV detector 
(which physically is on line, downline from the 
conductivity detector, see Figure 1) a very charac¬ 
teristic pattern for the four explosive’s residues 
can be obtained. These patterns can in turn be 
used to identify a particular explosive. This is the 
object of establishing a pattern characteristic of 
each individual low explosive. 

The next aspect of the study was to look at the 
cation pattern for the various low explosives. Of 
special interest was to determine if any ammonium 
salts were formed. Figure 10 shows the separation 
of some common cations and was used as a stand¬ 
ard. Figures 11, 12 and 13 shows the cation pat¬ 
terns of the four explosive residues. No significant 
ammonium was formed in any of the combustion 
products. The Pyrodex residue showed slightly 
higher levels of sodium than the other residues but 
even this is not significant. Other than this differ¬ 
ence there is little in the cation patterns to be of 
value in distinguishing the four explosives tested. 

Having established an anion pattern for the 
four low explosives another test was conducted in 
which this information could be applied to a 
case-like situation. Figure 14 is a photograph of a 


216 


























STANDARD CATIONS 


PYRODEX RESIDUE 


Eluent: 0.01 N HCI m 30% methanol 



0 5 10 15 20 

Minutes 


Figure 10. Separation of Common Cations. Peaks: Li + , 
lOppm; Na + , 10 ppm; NH + , 10 ppm; K + , lOppm. 


BLACK POWDER RESIDUES 


K + 




K + 



I-1-1-1-1 

0 5 10 15 20 

Minutes 

Figure 12. 1C Cation Pattern for Combustion Residues of 
Pyrodex. 

pipe fragment taken from an exploded pipe bomb 
which contained an unknown low explosive. The 
fragment was washed with 5ml. of distilled water 
and after filtering was analyzed by IC. 

Figure 15-a shows the water wash of the metal 
fragment while Figure 15-b shows the anion pat¬ 
tern of the potassium chlorate/sugar mixture. As 
can clearly be seen they are very similar. Figure 
15-a shows no similarity to any of the other anion 
patterns. 

A similar test was conducted with another pipe 
bomb containing another unknown explosive. A 
pipe fragment from the exploded pipe (Figure 16) 


Run 1 




I-1-1-1-1 I-1-1-1-1 

0 5 10 15 20 ° 5 10 15 20 

Minutes Minutes 

Figure 1 la,b. IC Cation pattern for Combustion Residues of 
(a) Home made Black Powder (b) Commercial Black Powder. 


217 


Figure 13. IC Cation Pattern for Combustion Residues of a 50/ 
50 Chlorate/Sugar Mixture for Two Separate Tests. 























FBT- 

i LABORATORY_«. 


Figure 14. Photograph of Pipe Bomb Fragment. 



was washed and analyzed by IC. Figure 17-a,b 
shows the results of this test. Figure 17-a is the 
chromatogram of the unknown residue which 
composes very favorably with a known Pyrodex 
residue anion pattern. 

A third test was conducted with a firecracker. 
Figure 18 pictures the type of firecracker on which 
the test was conducted and a small paper fragment 
which resulted from exploding a similar one. This 
small paper fragment was washed with 5ml. of 
water and the anion analysis conducted. Figure 
19-a shows the anion pattern of the firecracker. 
Of unusual interest is the intense concentration of 
nitrate in relation to sulfate. There is a difference 


Unknown Residue KCI0 3 /Sugar Residue 



Figure 15a. (a) IC Anion Pattern for Unknown Residue (b) IC 
Anion Pattern for Pyrodex Residue. 


Figure 16. 


in this pattern when compared to a known black 
powder anion pattern (Figure 19-b). One explana¬ 
tion of this difference is that there is incomplete 
combustion in the firecracker of the black powder 
yielding more unreacted nitrate than residue sul¬ 
fate. This is not uncommon when such small mix¬ 
tures of low explosives like black powder are used 
in a firecracker. 

In as much as the pattern failed to match any of 
the other low explosive, and the absence of any 
significant chloride peak which would be indictive 
of a chlorate or perchlorate based explosive, it was 
determined the firecracker contained a black pow¬ 
der mixture. A check of the pre-blast mixture re¬ 
vealed in fact it did contain black powder. 


Unknown Residue Pyrodex Residue 


Cl 



Figure 17. 


218 

























2/83 


Test Date: 




Figure 18. Photograph of Firecracker and Paper Fragment. 


These three examples illustrate the value of IC 
in analyzing explosive residues. In many cases the 
bomb crime scene is covered with debris of all 
sorts, which can act as contaminants in any 
analysis. IC analysis permits taking a small frag¬ 
ment from the device, which is free of contamina¬ 
tion and determining what the explosive main 
charge was. Although it is often difficult to find 
large pieces of a contaminant free device, it is not 
too difficult to find a dime size piece, free of con¬ 
tamination. 

The last two figures, Figures 20 and 21 show the 
relative similarity in several different tests of com¬ 
mercial and homemade black powder. With the 
exception of the pattern from the 10/28 test date 
(Figure 21) which shows a large amount of nitrate 
in the residue, virtually all the patterns are very 
similar. The difference in the 10/82 test date as we 
have noted previously can be due to incomplete 


Firecracker Residue Black Powder Residue 

so 4 - 2 



NOj- 



Minutes 

Figure 19. (a) IC Anion Pattern for Residue from Firecracker 
Paper (b) 1C Anion Pattern for Black Powder Residue. 



10/82 



Minutes 


month/year 



Figure 20. IC Anion Pattern for Commercial Black Powder 
Residues FOR THREE DIFFERENT TESTS. 


combustion occasionally seen in homemade black 
powders. 

In conclusion, it has been demonstrated that IC 
is a viable method for the evaluation and deter¬ 
mination of some low explosives. By developing 
an anion pattern characteristic of the low explo¬ 
sive identifications can be made of the individual 
explosives. Of the three basic explosives tested, 
black powder, Pyrodex, and chlorate/sugar all 
gave a fingerprint anion pattern which are individ¬ 
ually unique. 

In the future more testing of other low explo¬ 
sives will be conducted and additionally the 
formation of sulfide and thiocynate will also be 
examined. Due to problems experienced with the 
Dionex Electrochemical Detector these eval¬ 
uations were not completed during this series of 
tests. It is conceivable that through the evaluation 
of sulfide and thiocynate levels that commercial 
and homemade black powder residues could be 
differentiated. 



Minutes 

Figure 21. Anion Pattern for Home made Black Powder Resi¬ 
dues FOR FOUR DIFFERENT TESTS. 


219 


































































































» 
























































































IDENTIFICATION OF MONOMETHYLAMINE NITRATE AND 
MONOETHANOLAMINE NITRATE BY THIN LAYER CHROMATOGRAPHY 

G. F. Peterson,' M.S.; W. R. Dietz,’ B.S.; andL. E. Stewart, 2 Ph.D 


ABSTRACT. The sensitizers, monomethylamine nitrate (MMAN) and mono- 
ethanolamine nitrate (MEAN), contained in duPont and Hercules water gel explo¬ 
sives respectively, can be uniquely identified in evidentiary samples from bombings 
by utilizing the three thin layer chromatography (TLC) systems discussed in this 
paper. These TLC methods also identify the presence of other explosive ingredients 
and contaminants commonly found in debris from bombings. 

1 Chemists, U.S. Department of the Treasury, Bureau of Alcohol, Tobacco and Firearms, San Francis¬ 
co Laboratory Center, Treasure Island, California 94130 

2 Chemist, U.S. Department of the Treasury, Bureau of Alcohol, Tobacco and Firearms, National 
Laboratory Center, Rockville, Maryland 20850 

INTRODUCTION 

The identification of explosive residue in evi¬ 
dentiary samples from bombings, has been com¬ 
plicated by the proliferation of dynamite substi¬ 
tutes. Explosives sensitized with nitrostarch, nitro¬ 
cellulose, ethylene glycol mononitrate, aluminum, 
and alkylammonium nitrates are displacing explo¬ 
sives sensitized with nitroglycerin and nitroglycol. 

For example, in the mid-1970’s DuPont discon¬ 
tinued the manufacture of explosives containing 
nitroglycerin in favor of water gels. Parker (1975) 

Unlike most other ingredients in commercial ex¬ 
plosives, these modern sensitizers are often unique 
to explosives produced by one manufacturer, for 
example: 

—DuPont uses methylammonium nitrate 
(monomethylamine nitrate or MMAN) 

—Hercules uses ethanolammonium nitrate 
(monoethanolamine nitrate or MEAN) 

—Trojan used nitrostarch 
Thus, the type of explosive and its manufacturer 
can be identified if these sensitizers are detected. 

This paper describes thin layer chromatography 

Table 1 


System 

Development Solution 

Plate 

Sprays 

I 

chloroform/methanol/water 

(100:90:14) 

K2 

diphenylamine 
or ninhydrin 

II 

chloroform/methanol 

(7:3) 

K5 

fluorescamine 

visualization 

III 

chloroform/100% ethanol/water/HCl 
(100:90:5:3.5) 

K5 

ninhydrin 


systems by which the currently used alkylammoni¬ 
um nitrate sensitizers MMAN and MEAN can be 
uniquely identified. 

EXPERIMENTAL PROCEDURE 

When initial visual and microscopic examina¬ 
tions of debris fail to reveal the presence of an ex¬ 
plosive, then the entire sample of debris is ex¬ 
tracted. The debris can first be extracted with dis¬ 
tilled water and secondly with acetone or 
methanol. The extracts are filtered and evaporated 
to dryness. The water extract is redissolved in a 
small quantity of water for chemical spot tests. 
Feigl (1956) If the presence of nitrite or nitrate 
ions is detected with the Griess spot test, then the 
water and/or methanol extracts may contain 
MMAN or MEAN. These extracts are then pre¬ 
pared for TLC analysis by adding a few drops of 
the extracting solvent to the respective extract in 
order to redissolve and concentrate the explosive 
residue. The three TLC systems utilized in this 
procedure are shown in Table 1. 


221 






Screening for alkylammonium nitrates and con¬ 
firming the presence of ammonium, sodium, and 
potassium ions is performed using TLC System I. 
Primary amines and amino acids are visualized by 
spraying with ninhydrin. The ninhydrin solution 
consists of 0.2% ninhydrin in 0.1M citric acid, ad¬ 
justed to pH 5 with 2.0 N sodium hydroxide. Feigl 
(1956) Plates sprayed with ninhydrin are heated at 
100° C for 7 to 10 minutes to develop the color. 
The limits of detection for MMAN and MEAN, 
when sprayed with ninhydrin, are about 0.5 ug. 
Nitrates are detected by spraying the plates with a 
solution of 5% diphenylamine (DPA) in 95% 
ethanol followed by 10 minutes exposure to ultra¬ 
violet light and then spraying the plates with con¬ 
centrated sulfuric acid. Parker et al. (1975). The 
limits of detection for MMAN and MEAN, when 
sprayed with the diphenylamine/sulfuric acid 
combination are about 1.0 ug. Due to interfer¬ 
ences which may arise in this TLC system from 
some compounds (notably calcium salts from soil 
or explosives), and uncertainty in distinguishing 
MMAN and MEAN from each other, it may be 
necessary to also use one of the other TLC sys¬ 
tems, for the confirmation of MMAN and 
MEAN. 

If screening by System I indicates the presence 
of MMAN or MEAN, then fluorescamine deriva- 
tized amines are separated using System II. 
Primary amines and amino acids form intensely 
fluorescent substances when reacted with fluores¬ 
camine. This reaction proceeds rapidly at room 
temperature at pH 9. A solution of fluorescamine 
is prepared by dissolving 50 mg. of fluorescamine 
in 100 ml. of acetone. A 0.2 M borate buffer solu¬ 
tion is also prepared by dissolving 1.24 g boric 


acid in 100 ml distilled water. The pH of this solu¬ 
tion is adjusted to 9.0 by titrating with sodium hy¬ 
droxide. Nowicki (1976) A few drops of the redis¬ 
solved extract solution are placed into a well of a 
porcelain spot plate. Into each of these wells, two 
drops of the borate buffer solution are added fol¬ 
lowed by one drop of the fluorescamine solution. 
Upon completion of the reaction, the solutions are 
examined under ultraviolet light to observe the 
fluorescence. Those solutions which react posi¬ 
tively are spotted on K5 TLC plates and developed 
utilizing System II. The limit of detection for 
MMAN and MEAN is about 2.0 ug. This system 
gives an excellent separation of MMAN from 
MEAN. While MEAN and ammonia produce 
spots having similar Rf’s with this system, they 
can be distinguished from one another by using 
System III. 

System III, although slow, separates MMAN 
from MEAN with no interference from ammonia. 
Plates developed using this system are sprayed 
with ninhydrin. The developing solution must be 
prepared using 100% ethanol and concentrated 
HC1 since this system is sensitive to the concentra¬ 
tion of water. The loss of HC1 and the uptake of 
water reduce the efficiency of this solvent in three 
or four weeks. This system is especially useful 
when MMAN or MEAN are in very low concen¬ 
trations in the extract and may fail to be detected 
with System II. However, while high concentra¬ 
tions of amino acids streak in System III and can 
obscure the presence of MMAN and MEAN, 
amino acids remain at the origin in System II, thus 
eliminating their interference with MMAN and 
MEAN. Data for these three systems is presented 
in Table 2. 


Table 2 *RF’s (as%) 

Solvent System System I 


System II 


System III 


TLC Plate 

K2 

K5 

K5 

Compound 




MMAN 

40-56 

60 

31-37 

MEAN 

33-47 

39 

18-28 

Ammonium Nitrate 

31-46 

40 


Sodium Nitrate 

17-31 

— 


Potassium Nitrate 

10-14 

— 


n-Ethylammonium NO 3 

61-72 


37-38 

n-Propylammonium NO 3 

66-72 

73 

41-51 

n-Amylammonium NO 3 

77-88 

69 

48-66 

Iso-Propylammonium NO 3 

26-29 


41-55 

Iso-Butylammonium NO 3 

69-82 



l-amino-2-propanol NO 3 

52-61 

54 

36-38 

2-amino-l-propanol NO 3 

41-56 

42 

41-43 

2-amino-l-butanol NO 3 

55-68 

53 

41-45 


222 




Table 2 *RF’s (as %)—Cont. 


Solvent Svstem 


System I 


System II 


System III 


TLC Plate 

K2 

K5 

K5 

Anthranalic acid 

95-97 


95-97 

Phenylalanine 

44-67 

0 

5 

3,4-Dihydroxylphenylalanine 

1 

0 

49 

Tryptophan 

0-28 

0 

50 

Tyrosine 

0 

0 

50 

Norvaline 

40-61 

0 

50 

Ethionine 

47-61 

0 

49 

Isoleucine 

52-63 

0 

49 

Leucine 

47-78 

0 

50 

Methionine 

4-54 

0 

50 

Alanine 

14-27 

0 

41 

Arginine 

0 

0 

24-3 

Asparagine 

0 

0 

19-24 

Aspartic acid 

0 

0 

49 

Citruiline 

0 

0 

3-38 

Cystine 

0 

0 

25-28 

Glutamine 

5-14 

0 

49 

Glycine 

1 

0 

28-41 

Histidine 

0 

0 

16-23 

Lysine 

1 

0 

14 

Norleucine 

61-75 

0 

50 

Proline 

33-42 

0 

50 

Serine 

10 

0 

38-43 

Threonine 

0-22 

0 


Valine 

36-61 

0 

50 

3-Phenyl-l-propylamine 



69-76 

2-Amino-l -phenylethanol 



69-76 

Phenethylamine 



69-74 

Methamphetamine 



70-75 

Dextroamphetamine 



65-70 


*Rf’s are recorded as the Rf of the tail and the Rf of the leading edge. 

*tert amines, secondary amines, aniline, guanidine, hexamine, hydroxylamine, diphenylamine, urea, uric acid, etc., do not react 
with ninhydrin. 


CONCLUSION 

The use of these three TLC systems provides the 
necessary data for the unique identification of 
MMAN and MEAN. Ninhydrin and fluoresca- 
mine react with the primary amines. The diphenyl- 
amine/sulfuric acid spray combination and Griess 
spot test identify the presence of nitrate ions. The 
use of three different TLC systems increases 
specificity. In Systems I and III, compounds larg¬ 
er than ethanolamine nitrate, such as nitrates of 
alkaylamines, alkylamine alcohols, and aryla- 
mines, have greater Rf values than MMAN or 
MEAN. System II provides the separation of 
MMAN and MEAN from amino acids which re¬ 
main at the origin. 


REFERENCES 

Feigl, F. (1956). Spot Tests in Organic Analysis, 
Elsevier Publishing Co., Amsterdam, The 
Netherlands, pp. 284 and 327. 

Nowicki, H. G. (1976). Studies on fluorescamine. 
part I: applications of fluorescamine in foren¬ 
sic toxicological analysis, J. of Forensic 
Sciences, vol. 21, no. 1, pp. 154-162. 

Parker, R. G., Stephenson, M. O., McOwen, 
J. M. and Cherolis, J. A. (1975). Analysis of 
explosives and explosive residues, part 
1: chemical tests, J. of Forensic Sciences, vol. 
20, no. 1, pp. 133-140. 

Parker, R. G. (1975). Analysis of explosives and 
explosive residues, part 3: monomethylamine 
nitrate, J. of Forensic Sciences, vol. 20, no. 2, 
pp.257-260. 


223 























































MASS SPECTROMETRY METHODS 










ANALYSIS OF EXPLOSIVES BY LC/MS 


Jehuda Yinon 

The Weizmann Institute of Science 
Rehovot, Israel 


ABSTRACT. In many applications of forensic analysis, an analytical method is 
required which combines good separation characteristics with highly specific and 
sensitive detection. The Liquid Chromatography/Mass Spectrometry (LC/MS) 
system has such specifications and has an advantage over GC/MS in that it is suit¬ 
able for thermally sensitive and involatile compounds. We have interfaced an 
HPLC with a magnetic sector mass spectrometer. The mass spectrometer is a home 
built 90° 4-inch radius magnetic sector instrument with a high-speed differential 
pumping system. The HLPC consists of an Eldex High Pressure Pump, an Eldex 
Solvent Programmer, a Rheodyne Model 7125 Sample Injector and a Waters 441 
UV Detector. The column used was a RP-8 reversed-phase column. Mobile phases 
were methanohwater and acetonitrile:water at various relative concentrations. The 
LC/MS interface is a commercial Hewlett-Packard Direct Liquid Insertion Probe 
LC/MS Interface which is a variable split-type interface. A series of standard ex¬ 
plosive mixtures including TNT, RDX, Tetryl, NG and DEGN, as well as commer¬ 
cial explosives have been analyzed by this LC/MS system. LC/MS spectra of these 
explosives will be shown in order to demonstrate the usefulness of this technique in 
forensic analysis. 


When we talk about LC/MS, we have in the 
back of our mind GC/MS, which has achieved a 
remarkable success in qualitative and quantitative 
analysis. However GC has its limitations: GC, 
and therefore GC/MS is not suitable for thermally 
sensitive and involatile compounds, although 
techniques have been evolved to minimize these 
problems. 

HPLC however, has been shown to be a suc¬ 
cessful separation technique for thermally labile 
compounds. Judging from the number of papers 
on HPLC in this symposium it certainly is a suit¬ 
able method for the analysis of explosives. 

The main problem in LC/MS is to match a 
liquid at high pressure with the high vacuum of the 
mass spectrometer. An HPLC flow rate of 1 
ml/min results in a gas volume of 150-1200 
ml/min, depending on the solvents used. A Cl 
mass spectrometer can handle about 20 ml/min. 

Several interfaces have been designed [McFad- 
den (1979)], some of them are already commer¬ 
cially available. We have used in our system the 
Hewlett-Packard Direct Liquid Insertion Probe 
Interface [Melera (1980)] which is shown sche¬ 
matically in Figure 1. The LC effluent enters the 


interface and is split at the entrance of the ion 
source. Only about 1-2% of the effluent is al¬ 
lowed to enter the mass spectrometer, through a 
5pm aperture made in a stainless steel diaphragm. 
The droplets of the jet thus formed, are vaporized 
in a desolvation chamber, after which the solv¬ 
ent/sample vapor enters the ion source. The 
sample is ionized, the solvent serving as chemical 
ionization (Cl) reagent. 

The advantages of this interface are its relative 
simplicity and the fact that it can be used also for 
reversed-phase HPLC. Sample and solvent enter 
the desolvation chamber as droplets, which gives 
the sample a certain protection against thermal 
fragmentation prior to ionization. We obtain 
some type of direct chemical ionization, which 
makes this method in particular suitable for ther¬ 
mally labile compounds. The main disadvantage is 
that because of the effluent split, the sensitivity is 
reduced. The mass spectrometer we are using is a 
home built 90° 4-inch radius magnetic sector in¬ 
strument with a high-speed differential pumping 
system. The HPLC consists of an Eldex A-30-S 
pump, an Eldex programmer and low pressure 
valve, a Rheodyne 7125 Injector and a Waters 441 


227 



UV Detector. 

Figure 2 shows the entire LC/MS system while 
Figure 3 gives an insight into the ion source region 
through the glass seal. 

The heated desolvation chamber is made of 
MACOR glass-ceramic and serves as electrical in¬ 
sulation between the ion source which is at 1500 
Volts and the grounded interface probe. We have 
a cold finger cooled by liquid nitrogen to provide 
extra cryogenic pumping, but we have found that 
the system can also be operated without a cold 
finger. The performance of the system was found 
to be optimal when the source was not entirely 
closed, so that the local pressure in the ion source 
was not too high. This was achieved by having an 
opening in the source or by keeping the Interface 
Probe at a certain distance from the desolvation 
chamber. Although there is a high voltage insula¬ 
tion between the source and the interface probe, 
voltage breakdowns sometimes occur. The solvent 
vapor serves as electrical conductor. With acetoni¬ 
trile less breakdowns occur than with methanol. 
This problem does not exist in quadrupole mass 
spectrometers where the ion source is at ground 
potential or at low voltage. The HPLC column 
used was a Brownlee RP-8 reversed-phase 
column, Lichrosorb lOqm particle size, 4.6 mm x 
10 cm length. Mobile phases were methanohwater 
and acetonitrile:water at a flow rate of 1 ml/min. 


UV detector wavelength was 214 nm. 

When using the direct-injection type interface, 
we must be aware that large amounts of solvent 
but only a small amount of sample are introduced 
in the source. Solvent peaks can interfere with 
sample peaks, therefore the exact mass spectra of 
the solvents have to be known. 

Figures 4 and 5 show respectively the high pres¬ 
sure mass spectra of acetonitrilerwater (50:50) and 
methanohwater (50:50). Part of the mass 
spectrum in Figure 5 has been upscaled in order to 
demonstrate the possibility of solvent peaks inter¬ 
fering with sample peaks which are in the same 
mass range. Earlier experiments on the analysis of 
explosives by LC/MS have been done using nega¬ 
tive ions [Parker, Voyksner, Tondeur, Henion, 
Harvan, Hass and Yinon (1982)] and positive ions 
[Yinon (1983)]. 

The following examples demonstrate the use of 
this system for the analysis of several technical 
and standard mixtures. 

Figure 6 shows the HPLC-UV trace of a techni¬ 
cal mixture containing TNT + RDX with acetoni- 
trile:water (50:50) as mobile phase. Figures 7 and 
8 show respectively the LC/MS mass spectra of 
TNT and RDX. The mass spectrum of TNT in¬ 
cludes the MH + ion at m/z 228, typical adduct 
ions (M + CH 3 CN + H) + at m/z 269 and 
(M + 2CH 3 CN 4- H) + at m/z 310, an El fragment 


228 





















































Figure 2. LC/MS system. 



Figure 3. Ion source of LC/MS system. 


229 





~ 100 


llI 80 

o 
z: 

< 

§ 60 

3 
CD 

< 40 

LlI 
> 

< 20 
LlI 

or 

0 

0 10 20 30 40 50 60 70 80 90 100 120 140 

m/z 

Figure 4. High pressure mass spectrum of acetonitrile:water (50:50). 


LC/MS 

ACETONITRILE : WATER (50 50) 

CH 3 CNH + 

42 


h 3 o + 

19 


4 


( 2CH 3 CN + H ) + 
83 


2CH 3 CN + H 3 0 ) + 
101 


1 l 


142 

JL 


ion (M-OH)+ at m/z 210 and an abundant frag¬ 
ment ion (MH-30) + at m/z 198 mainly due to the 
reduction process to the corresponding amine 
[Yinon and Laschever (1981)] and partly to 
(MH-NO) + . The mass spectrum of RDX includes 
the MH + ion at m/z 223, the M + ion at m/z 222, 
the adduct ions (M + NO) + at m/z 252 and 
(M + CH 3 CN + H) + at m/z 264 and typical frag¬ 
ment ions (M-N0 2 ) + at m/z 176 and 
(MH-CH 2 N 2 0 2 ) + at m/z 149. 

Figure 9 shows the HPLC-UV trace of a techni¬ 
cal mixture containing RDX + PETN, using ace- 
tonitrile:water (50:50) as mobile phase. The mass 
spectrum of RDX is similar to the one in Figure 8. 
The LC/MS mass spectrum of PETN (Figure 10) 
contains the MH + ion at m/z 317 which can clear¬ 


ly be seen above the background noise. 

Figure 11 shows the HPLC-UV trace of a 
standard mixture of TNT and tetryl using metha- 
nol:water (50:50) as mobile phase. Figures 12 and 
13 show respectively the LC/MS spectra of TNT 
and tetryl. The mass spectrum of TNT includes 
the MH + ion at m/z 228, an adduct ion 
(M + CH 3 OH + H) + at m/z 260, the M + ion at 
m/z 227 and the El fragment ion (M-OH) + at m/z 
210 and the ion (MH-30) + at m/z 198. No molecu¬ 
lar ion was observed in the mass spectrum of 
tetryl, but only characteristic fragment ions at m/z 
241 (M-N0 2 ) + , m/z 225 (M-N0 3 ) + and m/z 224 
(M-HN0 3 ) + . Figure 14 shows the HPLC-UV 
trace of a standard mixture of nitroglycerin (NG) 
and diethylene glycol dinitrate (DEGN) using 


00 


uj 80 

o 

2 : 

< 

§ 60 
3 

CD 
< 


40 


LJ 

> 


< 20 


LlI 

or 


0 



h 3 o + 

19 

I?™* LC/MS 



METHAN0L-WATER(50 50)- 

-ch 3 + 



It 







(2CH 3 0H+H) + 




65 


_L 

h- A 

ll-.- *—H-1- 1 - 


10 


20 30 


40 50 

m/z 


60 


60 


(2CH 3 0H+H) + 

65 


LC / MS 

METHANOL WATER(50 50 ) 


(2CH 3 0H+CH 3 ) + (4CH 3 0H + H) + 

79 (3CH 3 0H+H 3 0) + '29 * 

115 

(3CH 3 0H+H)♦ 

97 


83 


~~1 

70 


80 


90 100 

m/z 


no 


3— 
120 


130 


Figure 5. High pressure mass spectrum of methanol water (50:50). 


230 


























RELATIVE ABUNDANCE ( % ) 


HPLC-UV TRACE OF TECHNICAL 
MIXTURE CONTAINING TNT+RDX 


COLUMN: RP-8 

ACETONITRILE :WATER(50:50),lml/min. 
UV-WAVELENGTH: 2l4nm 


RDX 



( mm. ) 


Figure 6. HPLC-UV trace of a technical mixture containing 
TNT+RDX. 


IOO 


80 


60 


40 


20 


,r/M* (MH ' N0)+ 
LC/MS |98 


0 


ACETONITRILE I WATER (50:50) 

TNT 


( M -OH) + 
210 


228 


(M+CH 3 CNH-NO) + 

239 


( MfCH 3 CNH) + 
269 


(M+2CH 3 CN*H) + 

310 


i I i i i i r 

0 220 230 240 250 260 270 280 290 300 310 

m /z 


170 180 190 200 2 


Figure 7. LC/MS mass spectrum of TNT with acetonitrileiwater as reagent. 


231 














































100 


Ld 80 

o 

§ 60 
z: 

3 

CD 

< 40 

Ld 
> 


Ld 

cr 


20 


0 


160 


(MH- 


ch 2 n 2 o 2 ) + 

149 


( M-N0 2 ) + 
176 


LC/MS 

ACETONITRILE : WATER (50:50) 

RDX 


MH + 

223 


M + 

222 


(M + N0) + 

252 (m-k:h 3 cnh) + 

264 


140 150 160 170 180 190 200 210 220 230 240 250 260 

m/z 

Figure 8. LC/MS mass spectrum of RDX with acetonitrile:water as reagent. 


HPLC-UV TRACE OF TECHNICAL 
MIXTURE CONTAINING RDX + PETN 

COLUMN: RP-8 

ACETONITRILE :WATER(50:50),lml/min 
UV-WAVELENGTH: 2l4nm 


RDX 



232 






































100 


lu 80 
o 

< 

9 60 


CD 

< 

LU 

> 


LU 

cr 


40 - 


20 


227 


ch 2 ono 2 

I 

o 2 noch 2 -c-ch 2 ono 2 

I 

ch 2 ono 2 


268 


272 


0 

220 230 240 250 260 


LC / MS 

ACETONITRILE-WATER (50 : 50) 

PETN 


MH + 
317 


_L 


LULL 


270 280 

m/z 


i r~ 

290 300 310 320 


Figure 10. LC/MS mass spectrum of PETN with acetonitrilerwater as reagent. 


methanohwater (50:50) as mobile phase. Figures 
15 and 16 show respectively the LC/MS mass 
spectra of NG and DEGN. The mass spectrum of 
NG includes a small MH + ion at m/z 228 and 
characteristic fragment ions (MH-CH 3 NO) + at 

HPLC-UV TRACE OF STANDARD 
MIXTURE OF TNT AND TETRYL 

COLUMN :RP-8 

METHANOL WATER(50:50), Iml/min 
UV-WAVELENGTH: 214nm 


TNT 



m/z 183 and (MH-HN0 3 ) + at m/z 165. The mass 
spectrum of DEGN includes a small MH + ion at 
m/z 197 and the fragment ions (MH-0) + at m/z 
181, (MH-HN0 3 ) + at m/z 134 and 



m/z 


Figure 12. LC/MS mass spectrum of TNT with methanol wa¬ 
ter as reagent. 



Figure 11. HPLC-UV trace of a standard mixture of TNT and 
tetryl. 


233 


Figure 13. LC/MS mass spectrum of tetryl with methanohwa- 
ter as reagent. 




































































HPLC-UV TRACE OF NG+DEGN MIXTURE 

COLUMN ' RP-8 

METHANOL: WATER (50. 50 ), Iml/min 
UV WAVELENGTH : 2l4nm 



Figure 14. HPLC-UV trace of a standard mixture of NG and 
DEGN. 

(MH-H0N0 3 ) + at m/z 118 which is the base 
peak. 

CONCLUSIONS 

In the direct liquid introduction method, be¬ 
cause only 1 % of the effluent enters the mass spec¬ 
trometer, about 2 orders of magnitude of sen¬ 
sitivity are lost. In our system, in order to obtain 
an identifiable mass spectrum, we needed to inject 
in the HPLC between 1-10 p<g sample. These 
amounts can be considerably reduced by using 
integration techniques or single ion monitoring. 
The Direct Liquid Introduction Interface is simple 
and can be easily accomodated on any mass spec¬ 
trometer with very little instrumental modifica¬ 
tion. The future of LC/MS is in micro LC/MS 
where flow rates are in the order of 10 /ul/min and 
where the entire effluent can enter the ion source 
without any splitting, and therefore without any 
loss of sensitivity. 


REFERENCES 

McFadden, W. H. (1979). Interfacing chroma- 


I00r 


u 80 - 
o 

o 60- 
z 
ZD 
CD 

< 40- 

UJ 
> 

£ 20 - 


(MH-HNOjP 

165 


cr 


183 


160 180 


LC/MS 

METHANOL. WATER(50 50) 

NITROGLYCERIN 

ch 2 ono 2 

chono 2 

I 


MH 

228 


200 

m/z 


220 


240 


SOURCE TEMP 90°C 

Figure 15. LC/MS mass spectrum of NG with methanol:water 
as reagent. 


100 


Qj 80 

u 

z 

< 

| 60 

ZD 

CD 

** 40 

lL) 

> 

£ 20 
_) 

UJ 

cr 


0 


(MH-HONO^)* 

116 


120 


H 2 C -0N0 2 
H 2 C 

- ON0 2 


140 


LC/ MS 

METHANOL WATER (50,50) 

DEGN 


(MH-0) 

181 


160 


180 


M H 
197 

_L 
200 


m/z 


SOURCE TEMP 75°C 


Figure 16. LC/MS mass spectrum of DEGN with 
methanohwater as reagent. 


tography and mass spectrometry. J. Chrom. 
Sci. 17: 2-16. 

Melera, A. (1980). Design, operation and applica¬ 
tions of a novel LC/MS Cl interface. Adv. 
Mass Spectr. 8B: 1597-1615. 

Parker, C. E., Voyksner, R. D., Tondeur, Y., 
Henion, J. D., Harvan, D. J., Hass, J. R. and 
Yinon, J. (1982). Analysis of explosives by li¬ 
quid chromatography - negative ion chemical 
ionization mass spectrometry. J. Forensic Sci. 
27: 495-505. 

Yinon, J. (1983). Forensic applications of 
LC/MS. Int. J. Mass Spectr. and Ion Phys. 
48: 253-256. 

Yinon, J. and Laschever, M. (1981). Reduction of 
trinitroaromatic compounds in water by chem¬ 
ical ionization mass spectrometry. Org. Mass 
Spectr. 16: 264-266. 


234 






























THE ANALYSIS OF POST-DETONATION 
CARBON RESIDUES BY MASS SPECTROMETRY 


A. S. Cumming, K. P. Park and M. R. Clench 
EM2 Branch 
RARDE 

Royal Arsenal East 
Woolwich 
London SE18 6TE 


ABSTRACT. In the forensic analysis of specimens from scenes of explosions it is 
normal to find some traces of the undecomposed explosive. However, it has 
proved impossible to detect and identify 2,4,6-Trinitrotoluene (TNT) in residues 
by the normal methods of swabbing followed by Gas Chromatography of the 
extract. As an oxygen deficient explosive TNT deposits carbon in the form of parti¬ 
cles on surfaces in the vicinity of the site of the explosion, and it was considered 
that this carbon could provide a means of identifying the explosive, since decom¬ 
position products from the detonation could well be trapped within it. Samples of 
carbon were examined by Mass Spectrometry using a pyrolysis probe. The detailed 
method of sample preparation will be described together with an account of the 
problems encountered. By flash heating the carbon sample in the pyrolysis cham¬ 
ber, which was directly connected to the Mass Spectrometer source, it was possible 
to examine the materials released. Our initial studies indicated that unreacted TNT 
was present and could be identified. These preliminary studies produced a success 
rate of 20% and further work has improved the technique considerably. This has 
included modifications to the probe design to permit its use in the Chemical Ionisa¬ 
tion and Negative Ion modes. The modifications and their effects will be described 
and the implications for the use of the technique with other carbon depositing ex¬ 
plosives such as RDX and PETN will be discussed. 


INTRODUCTION 

It is important for forensic purposes to be able 
to identify the material used in illegal devices. 
Normally some traces of undecomposed explosive 
remains after detonation, but it has proved ex¬ 
tremely difficult to detect and identify 2,4,6-trini¬ 
trotoluene (TNT) by the normal methods of swab¬ 
bing followed by Gas Chromatography of the ex¬ 
tract. 

It has been observed that although the detona¬ 
tion of TNT is very efficient, it deposits carbon in 
the vicinity of the explosion. The deposit normally 
takes the form of a film or particles of varying 
sizes. This behavior is also observed with other ex¬ 
plosives such as 1,3,4—trinitro— 1,3,5-triazacyclo- 
hexane (RDX) and tetra-methoxymethane tetrani- 
trate (PETN), though the carbon production is 
particularly pronounced with TNT, which is oxy¬ 
gen deficient. 


It has been postulated (1) that this carbon con¬ 
tains some nitrogen-containing compound or 
compounds resulting from the thermal decompos¬ 
ition of TNT not involved in the detonation. It has 
also been observed during in-house studies on the 
detonation of acetylene that organic materials are 
found in the carbon deposited by this reaction 
(Reference 2). 

It was considered that an investigation of the 
carbon deposited could lead to methods for de¬ 
tecting the typical explosion products of TNT and 
thence identifying it as the explosive found in for¬ 
ensic cases. The principal method used in this in¬ 
vestigation was pyrolysis—mass spectrometry, 
since it was considered that pyrolysis techniques 
offered the greatest likelihood of success in releas¬ 
ing trapped species held within or on the carbon, 
and that mass spectrometry would provide the 
most satisfactory means of identification. 


235 


SHIELD 


Pyrolysis is a technique which has become es¬ 
tablished for the characterisation of compounds 
which are either involatile or possess low volatil¬ 
ity, e.g. polymers (Reference 3). The Curie Point 
technique was the method used, in which the sam¬ 
ple is mounted on a ferromagnetic pyrolysis wire 
of known Curie Point. The wire is then placed 
within an Rf coil which is energised with high fre¬ 
quency current. The hysterisis losses from the in¬ 
duced magnetic field in the wire rapidly (1/2-ls) 
heat the wire to its Curie point. At this tempera¬ 
ture the level of induced flux is considerably re¬ 
duced giving much reduced heating in the wire. 
Consequently the temperature of the wire stabilis¬ 
es to within a few degrees of its Curie point as long 
as the coil is energised. 

Different alloys with different magnetic proper¬ 
ties have different Curie points, and therefore 
varying the composition of the wire allows a range 
of pyrolysis temperatures to be used. A tempera¬ 
ture of 1043K is produced by a wire of 100% Fe, 
while an alloy of 50.6% Fe and 49.4% Ni w/w 
gives a temperature of 783K. 

EXPERIMENTAL 

Mass Spectra were obtained with a VG Micro¬ 
mass 16F single focussing magnetic sector instru¬ 
ment. The ion source is fitted with four re-en¬ 
trants, one for direct liquid injection, one for the 
solids probe, and two for GC effluents. 

Pyrolysis-Mass Spectrometry (py-MS) was car¬ 
ried out with the VG Organic Pyroprobe, using a 
modified Pye Unicam Rf coil and controller. The 
probe is inserted through the airlock provided for 
the solids probe and butts directly on to the source 
by means of a ceramic cone. Volatile pyrolysis 
products pass directly through the centre of the 
probe, as a result of the pressure difference, and 
enter the source. The probe assembly is shown 
schematically in Figure 1. The wire is mounted in 
the holder and fitted with the shield shown in Fig 
2, before loading into the probe. 

The method of preparing carbon samples for 



WIRE 



1 

2 

3 

U 

5 

cms 






Figure 2 

analysis depends on the type of deposition. For 
example if the carbon particles are deposited on 
metal surfaces it is relatively easy to scrape them 
off and test them without further preparation. 
Two other examples of carbon deposition were 
studied and methods for sample removal devel¬ 
oped: 

(1) From cloth. 

The recovery was carried out as follows: 

(a) The samples were cut into small squares (4 
cm 2 ) 

(b) Each sample was held in a No. 4 glass sinter 
fitted to a Buchner flask under suction and repeat¬ 
edly washed with distilled water. 

(c) When all the carbon had been removed and 
collected in the sinter, it was dried in an oven at 
353K for 20 minutes before being stored for analy¬ 
sis. 

(2) From wood 

(a) The blackened surfaces were scraped and 
the resulting fragments collected. 

(b) These fragments were placed in a clean dry 
centrifuge tube to which Analar Acetone was 
added. 

(c) The sample was placed in an ultrasonic bath 
for approximately fifteen minutes. 

(d) The sample was centrifuged, the solvent de¬ 
canted and re-used. 

(e) The carbon was collected, dried as previous¬ 
ly described and stored for analysis. 

Before use the pyrolysis wires were cleaned by 
passing them through the flame of a butane micro¬ 
burner. A pyrolysis temperature of 1043K (770C) 
for 3 seconds was used for all the experiments, 
with the probe maintained at 473K. 

Prior to the investigation of actual samples ref¬ 
erence pyrograms of both TNT and carbon were 
obtained under the same conditions as used for the 
samples. Wires were coated with TNT or activated 
charcoal and pyrolysed. 


236 




























The samples of carbon to be examined were 
coated on to the pyrolysis wire by preparing a slur¬ 
ry with distilled water and dipping the cleaned 
wire into it. It was found that the carbon adhered 
to the wire after drying so that a sample of about 
0.05 mg could be inserted into the probe and pyro- 
lysed. 

Initially the mass spectrometer monitored the 
region of 40-120 atomic mass units (amu) but it 
soon became evidence that the carbon in many 
cases contained undecomposed TNT, so that the 
base peak of TNT (m/z 210) could be used for sin¬ 
gle ion monitoring. 

RESULTS AND DISCUSSION 



100 

80 

60 

40 

20 

0 


40 



The mass pyrogram of TNT is shown in Figure 
3. The different peaks correspond to surges in the 
probe internal pressure, and the length of time be¬ 
tween pyrolysis and the products reaching the 
source. The mass spectra corresponding to the 
peaks a, b and c are shown in Figure 4. 

In the analyses of post detonation carbon, TNT 
itself was found in 20% of the samples examined 
(out of a total of 40). The pyrogram of a success¬ 
ful run is shown in Figure 5, and the mass spec¬ 
trum of each peak in Figure 5 is shown in Figure 6. 
Some material other than TNT is evolved, as can 
be seen. However, in the unsuccessful analyses no 
significant ion current was observed at m/z 210. 
This was also true of the examination of the car¬ 
bon blanks. 

The results obtained in this study were surpris¬ 
ing in that it was not expected that TNT itself 
would be found, rather that decomposition prod¬ 
ucts resulting from the detonation of the explosive 
would be present within the carbon. 

Spectra obtained from the pyrolysis of both 
TNT and the contaminated carbon differ from the 



MASS SPECTRA OF PEAKS IN FIG 3 


Figure 4 (a)(b)(c) 


standard TNT mass spectrum in Figure 7 in one 
respect: the Molecular Ion at m/z 227 is greatly 
reduced in intensity if not completely absent. This 
is probably accounted for by the high energy used 
in pyrolysing the sample, leaving the molecules in 
an excited state on entering the source. This would 
assist the ortho effect in the initial fragmentation 
of 2,4,6-TNT as described by Bulusu and 
Axenrod (4). The peak at m/z 210 is the normal 
100% or Base peak in the electron impact spec- 



Figure 3 Mass Pyrogram of TNT 


Figure 5 Mass Pyrogram of Successful Analysis 


237 
































Figure 6 (a)(b)(c)(d) 


trum of TNT. However, since the same effect is 
observed for both sample and standard, the ab¬ 
sence of the M + ion does not affect the identifica¬ 
tion of the explosive present. 

It is difficult to estimate the levels of TNT in the 
carbon samples since calibration with post-det¬ 
onation carbon is impossible, and doped samples 
do not simulate experimental conditions. It has 
been found that doped samples thermally desorb 
explosive prior to pyrolysis, but that little or no 
desorption takes place with test samples. This 
indicates that the TNT is not merely present as a 
loosely bound surface layer, but is more firmly at¬ 
tached to the carbon, either strongly adsorbed on 
active sites on the surface or perhaps trapped with¬ 
in the carbon by means of a process analogous to 
matrix isolation (5) which would limit the oppor¬ 
tunities for further decomposition. This would ac¬ 
count for the problems encountered using tradi¬ 
tional analytical methods. Its liberation within the 
pyrolyser must then depend on the rapid expan¬ 
sion of the gases in the carbon when heated by the 
Curie point wire, causing the carbon to decrepitate 
and the TNT vapour to escape. 

The method described shows great promise for 
the determination of the presence of TNT in de- 



Figure 7 


238 




















































bris. The one in four success rate probably reflects 
two factors: 

(a) The non-uniform dispersal of the TNT in 
the carbon deposited, leading to high localised 
concentrations and difficulties in sampling. 

(b) Inefficiences in the removal of carbon from 
debris, and its subsequent analysis. 

Considerable work is being carrried out at pres¬ 
ent on the second factor, principally on modifica¬ 
tion to the probe to increase its effectiveness. 

As supplied, the probe relies on the pressure dif¬ 
ference between the sample chamber and the 
source to draw the pyrolysis products into the 
mass spectrometer. This arrangement does not 
permit the use of either Chemical Ionisation or 
Negative Ion modes, both of which require a 
significant gas pressure within the mass spectro¬ 
meter source. There are distinct advantages in us¬ 
ing these modes, especially Negative Ion, which is 
selective for electron capturing materials (6). 
Therefore a modification to the probe was de¬ 
signed so that a controlled bleed of a gas could be 
supplied to the base of the pyrolysis chamber and 
thus provide a ‘carrier’ to flush released volatiles 
into the source not only in Cl or NI but also in the 
Electron Impact mode already studied. An addi¬ 
tional benefit of this modification is the reduced 
likelihood of contamination of the probe. 

Initial tests indicated that the modification does 
provide a distinct improvement and that negative 
ion operation is possible. The identity of the car¬ 
rier gas appears to be important, the best results 
being obtained with gases such as hydrogen which 
may act not merely as a carrier but also as a re¬ 
agent in the same manner as in the Cl mode. 

The availability of the negative mode will in¬ 


crease the likelihood of detecting RDX and PETN 
within post detonation carbon. Both of these ma¬ 
terials are much less stable in the mass spectro¬ 
meter than TNT, and give El spectra with a base 
peak of m/z 46. The interferences present in most 
samples make monitoring of this ion inconclusive 
in the El mode. The selectivity of the negative 
mode should make the identification of residues 
from both of these possible. A full report on the 
result of these researches will appear in due 
course. 

CONCLUSIONS 

The technique has the potentiality to become an 
extremely useful method for the analysis of post 
detonation residues, not only for traces of TNT 
but for other carbon depositing materials as well. 
A great deal of work remains to be done, but it 
should be possible to devise a routine method of 
analysis. 

REFERENCES 

/. Ornellas D L, McGuire R R; Laurence 
Livermore Lab Report CIO 18211 1979. 

2. Chase J D; Ph.D.Thesis, University of London 
1973. 

3. Wolf C J, Grayson M A, Fanter D L; Anal 
Chem 1980 52 (3) 348A. 

4. Bulusu S, Axenrod T; Organic Mass Spectro¬ 
metry 1979 14 585. 

5. Dunkin IR; Chem Soc Rev 1980 9(1) 1. 

6. Yinon J, Zitrin S; The Analysis of Explosives, 
Pergamon Press, Oxford 1981. 

Copyright: © Controller, Her Majesty’s Station¬ 
ery Office, London, 1983. 


239 
























































































ON-LINE COMPUTER SEARCH 
SYSTEM APPLIED TO EXPLOSIVES 


Harold R. Messier 
Chief Criminalist 
Metropolitan Police Laboratory 
St. Louis, Mo. 63103 


ABSTRACT. The analysis of explosive residues by electron impact gas chro¬ 
matography mass spectrometry and on line computer searching of spectra will be 
presented. A microprocessor based GC/MS system and related software was used 
to approach the problem. Real time computer searching of G.C. peaks utilized a 
pre-selected library of explosive spectra. Methods of sample collection and prep¬ 
aration will be reviewed. For centuries chemists have pondered ways to analyze 
substances and success would only bring fleeting moments of joy until the chemist 
was back at the bench trying to improve his methods or yields. At some point in 
time it becomes necessary to assimilate the research data and implement a simple 
and reliable method of routine analysis on a regular basis. These methods ideally 
will be governed by the quality of data, economics of the test and intra-laboratory 
reproductibility. Our laboratory had access to a small GC/MS which had proven 
itself quite valuable for drug analysis over the last five years. The instrument is ex¬ 
tremely simple to operate and an untrained analyst can usually run a sample by 
themselves after a few hours training. The down time on our system was about 
10%. Data collection, tabulation and library searching was achieved with a micro¬ 
processor. 


EQUIPMENT 

Equipment consisted of a Hewlett Packard, 
Model 5992A GC/Mass Spectrometer containing 
an electron ionization source and quadrupole 
mass analyzer used to collect standard spectra. 
The instrument is controlled by a 9825A micro¬ 
processor, having a 16K memory. 

SOFTWARE 

Software used was Hewlett Packard’s On-Line 
Search Tape, Part #05992-10012, supplied with 
the instrument. On-Line Search software allows 
the 5992 GC/MS to perform scanning experiments 
where a library of up to 50 compounds is searched 
as each GC peak elutes. The results of the search 
are printed with the peak height and correlation 
factor on the chromatogram plot. Operating soft¬ 
ware and spectral libraries are stored on a single 
magnetic cartridge. 

Background correction is performed automat¬ 
ically. The background taken from the previous 
valley between peaks is subtracted from the peak 


spectrum and the stripped spectra for each peak is 
saved for later tabulation or search with an 
off-line library. 

The software was modified by our laboratory to 
accommodate a single library with a capacity of 
1,299 pollutants and explosives. The library spec¬ 
tra are stored as the 10 most significant peaks 
where significance is defined as mass times abun¬ 
dance. 

Library entries were added by chromatograph¬ 
ing standard explosives and by keyboard entry, us¬ 
ing values abstracted from the literature. With ex¬ 
perience only about 15-20 masses and their abun¬ 
dances have to be entered for selection of the 10 
most significant peaks. 

RESULTS AND DISCUSSION 

EI-GC/MS is helpful in identifying some explo¬ 
sives. Data handling capabilities supplied by the 
microprocessor are adequate for normal qualita¬ 
tive runs. The method of building a library on the 
ten most significant peaks allows the library to be 


241 


stored on smaller space. Searching an unknown, is a simple operation on a small computer and 

reduced to ten peaks against a library of ten peaks, could be easily adapted to available equipment. 


Table 1. PROGRAM MODIFICATIONS TO ON LINE SOFTWARE TO LENGTHEN OFF LINE LIBRARY #1 TO 1299 
SPECTRA 


From SIM tape or appropriate tape copying program, create a new copy of an “ON-LINE-TAPE” files 0-24. 

Erase tape copying program ERASE a EXECUTE 

Locate NULL File (A computer generated file indicating end of valid files) 

fdf 25 


Mark the remainder of tape for correct file lengths of library segments (13 files of 4400 bytes each, 100 library entries each file) 

mrk 13,4400 


Allocate space in memory for libraries 

dim L [550] 

(L (550) = size of array, derived from each data file being 4400 bytes long and each element of the array being 8 bits long: = there 
are 4400/8 = 550 elements in each array in each file.) 

Load data file of desired library in to active memory of computer from original tape , write PROTECT THIS TAPE AS IN 
COPYING PROGRAM. 


ldf X, L [*] 

(files 25-28 contain original 400 drug entries; files 29-37 contain original 900 pollutant entries; L (*) denotes entire data array.) 
Record data file onto new tape on desired file 


ref Y, L [*] 

Repeat for subsequent data files to be moved to make a pollutant library 1299 Spectra long transfer: 


FILE 


Original Tape 


New Tape 

29 

to 

25 

30 

to 

26 

31 

to 

27 

32 

to 

28 

33 

to 

29 

34 

to 

30 

37 

to 

31-37 


The above operations will transfer the 517 pollutants held in Library 2 of the 5992 GC/MS ON-Line tape to locations in Li¬ 
brary 1 on a copied tape and leave remaining 782 entries available for entry of data of interest. The following operations will adjust 
parameters used by the system for library searching and modifying. 

From Manager ON COPIED TAPE obtain systems comments. File 11 contains “GC,MS, and system status save files.” 

Clear existing program ERASE a EXECUTE 
Type 


dim X [18], V [20], G [16], S [10], R, T EXECUTE 
ldf 11, X [•], V [*], G [*], S [*], R, T EXECUTE 
1299- V [14] EXECUTE 
0- V [15] EXECUTE 

ref 11, X [*], V [*], G [*], S [*], R, T EXECUTE 

The above allocates space for the arrays defined above, loads them in their entirety, alters some variables (V [14] and V [15]) to 
allow OFF-LINE Library 1 to be 1299 Spectra long with Library 2 of 0 length. Then re-records this information onto the tape in 
File 11. 

When adding spectra you must replace as opposed to append. The variables controlling the append operation apparently can¬ 
not be altered appropriately. 

PROGRAMMING BY: Criminalist Victor Granat 


242 


SPECTRUM 21 LIB 2 RBX 


Ret.T1 n e= 6.3@ Res po nse Factor* 1.8 d 


RDX 


M.W 


NO*. 

i 

M 

r t 

N N 

CjN'' v ''N0 i 


" **i-1-1-1~i-j- i — 

50 100 


i-j-1-1 “ 

150 


1 ”1. 

200 


■ “1 "■ * 

250 


*t «* - 

300 


-1 -I —■ ~l — - 

350 


• -»” "i 

400 


E n t r y 

Mass 

Abundant 

1 

41 

253 


42 

891 

3 

46 

1000 

4 

55 

91 

5 

56 

278 

b 

71 

108 


t J 

323 

8 

8 2 

83 

9 

120 

80 

10 

128 

127 

SPECTRUM 24 

LIB 2 


2t 6-DMT 


-"»—•*■*-'< 

-1-! 

_ 3 — ~*j — —j — 


5 0 

100 

Ent rv 

Mass 

Abundance 

1 

63 

720 

j 

77 

400 

3 

78 

328 

4 

89 

630 

C 

J 

90 

478 

6 

91 

270 


121 

230 

8 

135 

170 

9 

148 

240 

18 

165 

1 000 

SPECTRUM 25 

LIB 2 T 


Ret. T i fte = 0. 0 0 Re s p ouse Faetor* 1.08 

CH a 

2^-DNT 


t ■ —| -l —*-»-1 - 

150 


1 ‘ — ~t-i-1 *— ”1 --j- 

200 258 


—»“ -•[ ~l-j- 

300 


- -1 — -1 —1. 

358 


- -l ~~ •] 

400 


Ret.Time* 0.00 Response Factor* 1.00 



58 

100 

ry 

Mass 

Abundance 

1 

63 

570 

p 

76 

C i' 0 

3 

89 

670 

4 

134 

200 

5 

149 

140 

b 

164 

1 10 

7 

180 

150 

8 

193 

150 

q 

210 

1 000 

10 

211 

80 


...... ...| ... t 


-1- 

150 


200 


2,4,6-TNT 

tA.w- 



I-1-1-1-! ™ ."j — “ 

250 300 


"t-j 

35& 


“ -i-»-J 

400 


Figure 1. Mass spectrum of three explosives as they appear in the library search program with their ten most significant peaks. 


243 





















TETRYL (NITROMINE) 


FRH 


3069 LSN 


7 [ 


6.3 MW 


C7 .HE.HE .08 


\ TOTAL 



Figure 2. Mass Spectrum of Tetryl from the literature about to be coded. Note reference lines drawn at 40, 20 and 10% abundance. 


Of f.!.... 

i n e L. i b r a r 

v b. d i t i n 3 b' r o 3 r 13 . pi l; 

reo 10 / 

•”| o ..• "7 "1 

I n d 0 x 

Mass 

h b u n d M a s s M b u n d a n c €• 



i 

125 


•■**» *“» i::r 
•«« r • J 



•"i 

u. 

12 6 


25 3150 



•J 

| b *7 

<S. i...- i 


100 12700 



4 

128 


18 2304 



ir 

•J 

129 


i o b o 45 0 

••• v (•*... C... 



b 

130 


3 390 



r 

.L i O 


80 13840 



1^1 

174 


1 O *7 O £' 0 

*»• 'w 1 i!... Cm* 



9 

175 


1 175 



10 

•j *7 

X 1 C,„ 


3 516 



11 

150 


14 2100 



1 2 

148 


14 2072 

* 


1 3 

115 


70 8050 



14 

•*~i —;i 

r r 


20 1540 



1 l J 

116 


1 1 *i*k* 2 !.... 



Mo lee 

u 1 a r N e 

i 3 h t :r 1 7 8 „ 1 R 0 1■=• n 

t i o n I n 

d S X 0 „ 0 0 

Ent rv 

M a s s 

h b 

u n d a n c 0 M a s s * H b u n d 

a n c e N 

o r i v i „ H b u n d „ 

1 

i* r 


0 15 4 0 


200 

fcm 

115 


70 8850 


700 


126 


25 3150 


250 

4 

I -'j "7 

J. C... 1 


100 12700 


1 0 0 0 

Cj 

128 


18 2304 


180 

6 

129 


*j O ’ O O O 


180 

”*;i 

1* 

148 


14 2072 


14 0 


150 


14 2100 


140 

9 

*j ~i 

J. 1 


80 13840 


800 

10 

174 


13 2262 


130 

ii b 0 6 

8 p o o 1.1-" 

U i v l 

R 0 0 l'“ d €' d 1 ft L 1 b i" 0, T Y 

1 a s 0 

nt rv\ # 528 N 


Figure 3. Keyboard entry of 1-Mononitronapthalene and the ten peaks selected by the microprocessor. 


244 































SMOKELESS POWDER IDENTIFICATION 


Roger M. Martz, B.S. 
Special Agent 

Chemistry/Toxicology Unit 
Scientific Analysis Section 
FBI Laboratory 

9th & Pennsylvania Avenue, N.W. 
Washington, D.C. 20535 

Lynn D. Lass well III, B.A. 
Special Agent 

Chemistry/Toxicology Unit 
Scientific Analysis Section 
FBI Laboratory 

9th & Pennsylvania Avenue, N.W. 
Washington, D.C. 20535 


ABSTRACT. Until recently, forensic comparisons of smokeless powders were 
made based upon physical properties ( e.g ., size, shape, color) and positive matches 
would be tenative, especially in the case of burned residues. For the last several 
years, comparison and identification of both burned and unburned smokeless 
powder residues have been done in the Federal Bureau of Investigation Laboratory 
by a combination of physical comparison and chemical analysis using high perfor¬ 
mance liquid chromatography. Examining both the chemical and physical proper¬ 
ties of the smokeless powders allows a more definitive comparion or identification. 
This presentation will describe a new technique for comparing and identifying 
smokeless powders based upon the analysis of the trace organic constituents by 
capillary column GC/MS. The chemical examinations consist of extracting the 
powder or powder residue with chloroform, and separating and identifying the sol¬ 
uble constituents with a fused silica capillary column GC/MS system equipped 
with a cold on-column injector. Although this procedure can resolve smokeless 
powder extracts into as many as 30 major and minor components, only the major 
components are used for the chemical comparisons. On our GC/MS data system, 
we have established a smokeless powder “library” (representing about 100 pow¬ 
ders) with each entry being a composite spectrum generated by merging the spectra 
of the major peaks found in the powder extract. Identification of a smokeless pow¬ 
der is effected by computer searching the composite spectrum of the questioned 
powder against the library. Confirmation of the computer identification is made 
by comparing the relative amounts of the various components as found by the 
GC/MS analysis, and by comparison of the physical properties of the known and 
questioned. 


SMOKELESS POWDER IDENTIFICATION 

Smokeless powders are frequently encountered 
in the Federal Bureau of Investigation Laboratory 
in connection with improvised explosive devices 
(IEDs)—both exploded and unexploded. The 
identification of the smokeless powder or powders 


used in the IED is useful for lead purposes and to 
help characterize the IED and link it to other simi¬ 
lar devices. The comparison of smokeless powders 
is vital when a reloading powder is found in a sus¬ 
pect’s possession and a link is sought between the 
suspect’s powder and that used in the IED. 


245 


Smokeless powders contain various organic 
components such as explosives, plasticizers, stabil¬ 
izers and retarders. The analysis of these volatile 
organic compounds can assist in the comparison 
and identification of smokeless powders. Many 
different procedures are available to compare the 
constituents of smokeless powders, these include 
gas chromatography, liquid chromatography, 
thin-layer chromatography, nuclear magnetic res¬ 
onance, etc. (Trowell and Philpot (1969), Mach et 
al. (1978), Newlon and Booker (1979), Hardy and 
Chera (1979) and Meyers and Meyers (1983)). 

We have developed a technique which uses in¬ 
jection directly on column, separation on a fused 
silica capillary column, detection by mass spec¬ 
trometry and data analysis by computer to com¬ 
pare and identify smokeless powders. A compari¬ 
son of two smokeless powders is a straightforward 
peak for peak comparison of the reconstructed to¬ 
tal ion chromatograms (TICs) of the two samples’ 
volatile components. The same compounds must 
be present in the same ratios for two smokeless 
powders to be considered to have originated from 
a common source. 

The identification of smokeless powders is 
based on the same comparison technique; how¬ 
ever, the TIC of a questioned smokeless powder is 
compared with the TICs of all previously run 
known smokeless powders. The actual compari¬ 
son of a questioned sample against all the known 
samples which have been run is simplified consid¬ 
erably by using the library search software avail¬ 
able on the gas chromatograph/mass spectrometer 
(GC/MS) data system. We will present data which 
illustrate the results obtained by using this com¬ 
bination of chromatography hardware and data 
system software to facilitate these comparisons 
and identifications. 

MATERIALS 

The smokeless powders used in this experiment 
are all reloading powders. They were obtained di¬ 
rectly from the manufacturers over a period of 
several years. 

EQUIPMENT 

The GC/MS used is a Finnigan 4021 quad- 
rupole/mass spectrometer equipped with a Finni¬ 
gan INCOS 2300 data system. The gas chromato¬ 
graph was equipped with a Scientific Glass Engi¬ 
neering, Inc., on-column injector and a 20-meter, 
0.20 mm ID, SE-54 bonded phase fused silica col¬ 
umn. The column was extended through the sep¬ 


arator oven to within several centimeters of the 
mass spectrometer ionization source. 

EXPERIMENTAL CONDITIONS 

Several particles of a smokeless powder (disc, 
cylinders, ball, flake, etc.) are extracted with 0.5 
ml of chloroform for 10 minutes with vortexing. 
The unconcentrated sample is injected (0.1 to 
0.2ul) on-column at ambient temperature outside 
the gas chromatograph oven. The on-column in¬ 
jector is then introduced into the oven and the 
oven temperature is programed at the maximum 
rate (approximately 20° min) from 70° to 265°. 
The carrier gas is helium (1 ml/min). 

All spectra were obtained under electron impact 
conditions using the following parameters: 


Mass range 

45 -400 AMU 

Scan rate 

1 sec/scan 

Electron ener¬ 


gy 

70 eV 

Filament 

0.4 mA 

Multiplier 

1250 V 

Dynode 

3000 V 

Amplifier 

1 X 10' 7 A/V 

Source press 

1 x 10' 7 torr 

Source temp 

350° 

Transfer line 

250° 


Results 

Known samples of smokeless powders are 
treated as in the experimental section and the re¬ 
sulting TICs are processed with the data system to 
create a user-generated library of smokeless pow¬ 
ders. Processing the data involves summing the 
mass spectra of all the components of interest and 
subtracting the contribution due to background. 
The resulting summed (or composite) spectrum is 
made a library entry characteristic of the smoke¬ 
less powder run. This composite spectrum will 
represent both the volatile organic components 
and their relative concentrations through the pres¬ 
ence and intensities of the ions in the summed 
spectrum. We have processed approximately 80 
different known smokeless powder samples and 
currently have approximately 150 separate entries 
in our library of smokeless powders. 

A typical smokeless powder (Hercules 2400) will 
be used as our first example both to illustrate how 
the library was prepared and how a search of the 
library is conducted. The TIC of the Hercules 
sample is shown in Figure 1. The major com¬ 
pounds detected are identified as nitroglycerin, 
diphenylamine and ethyl centralite. These corn- 


246 


100 . 0-1 


211 


HERCULES 2400 


RIC 


6 


392 


298 


100 

1:40 


200 

3:20 


— r~ 

300 

5:00 


I 

400 

6:40 


—( 

500 

8:20 


600 

10:00 


700 SCAN 
11:40 TIME 


Figure 1. Total ion Chromatogram of Hercules 2400 


pounds were identified by their mass spectra (Fig¬ 
ure 2A, 2B, 2C). The spectrum which results from 
the summation of scans 187 to 413 followed by the 
background subtraction of the sum of scans 97 to 
185 is illustrated in Figure 3. The peak at 46 AMU 
is from the nitroglycerine and is clearly dominant 
in this composite spectrum as it is in all dou¬ 
ble-based smokeless powders. To de-emphasize 
the nitroglycerine contribution a summation was 
made from scan 289 to scan 421 followed by back¬ 
ground subtraction (Figure 4). This composite 
spectrum, which omits the nitroglycerine contri¬ 
bution, exhibits major ions due to the 
diphenylamine and ethyl centralite. These ions 
were suppressed in the presence of the nitrogly¬ 
cerine ions by the normalization procedure of the 
data system. 

If either of these summed spectra is searched 
through our library of smokeless powders then a 
match with Hercules 2400 (Figures 5, 6) results. 
The library includes entries made using exactly the 
same technique both with and without the nitro¬ 
glycerine data. The TICs of all the known samples 
are also stored by the data system for direct com¬ 


parison with the questioned samples. 

Comparison of Norma N-200 smokeless pow¬ 
der (Figure 7) with the Hercules 2400 powder is 
done as an instructive exercise (Figure 8). It is ob¬ 
vious that the volatile components of the two 
smokeless powders allow ready differentiation be¬ 
tween them using this experimental technique. As 
usual it is easier to determine that two things are 
different than it is to determine that they are iden¬ 
tical. 

The actual identification of an unknown smoke¬ 
less powder is our goal and when a summed spec¬ 
trum for the Norma N-200 (Figure 9) is searched 
through the library the most probable identifica¬ 
tions are listed (Figure 10). In this case, as would 
be expected, the entry for Norma N-200 was listed 
first. If the sample’s origin had been unknown 
then a comparison of its TIC with the TIC previ¬ 
ously obtained for Norma N-200 would be made. 
A comparison of the TIC of the second best match 
with that of the Norma N-200 TIC would easily 
convince the examiner that of all the known sam¬ 
ples which have been run, Norma N-200 is the 
best match. 


247 














46 



Figure 2a. Mass Spectrum of Scan 211 (Nitroglycerine) 


The Norma and Hercules smokeless powders 
are chemically similar to other smokeless powders 
in their respective “families” and in some in¬ 
stances to eliminate similar computer matches it is 
prudent to physically compare the questioned 
smokeless powder with the known samples to dif¬ 
ferentiate between close matches. Parameters 
which can be compared include shapes such as 
ball, disc or cylinder, as well as dimensions of the 
various shapes. The data system library search 
routine allows spectra to be searched under con¬ 
straints of molecular formula and/or molecular 
weight range. Our composite spectrum does not 
have a chemical formula or a molecular weight so 
these fields can be used to represent the physical 
shape of the smokeless powder. Letters allowed by 
the data system including “C”, “O” and “N” 
which normally represent carbon, oxygen and ni¬ 
trogen in molecular formulas. These letters now 
represent particles with cylinder, ball and disc 
shapes respectively. In the Norma N-200 sample 
the “C” in the area reserved for the molecular 


formula in the library search routine denotes a 
clyndrical particle. 

The molecular weight entry in the smokeless 
powder library is actually a measurement of per¬ 
tinent dimensions of the various smokeless pow¬ 
der shapes. In the Norma N-200 sample “293” in¬ 
dicates a powder with an outside diameter of 0.029 
inches and a length of 0.03 inches. This conven¬ 
tion applies to both cylinders and discs. In the case 
of ball-shaped particles the diameter in thou¬ 
sandths of an inch is entered. 

In order to be more specific in our computer 
searches the shape and dimensions (or range of 
dimensions) can be specified. This eliminate the 
need for searching the entire library. The searches 
in the above examples were done with no restric¬ 
tions so that the entire library would be searched. 

While the emphasis of this paper is on the data 
system techniques involved, one of the most im¬ 
portant pieces of hardware is the on-column injec¬ 
tor. This injection system allows the introduction 
of the smokeless powder extract on to the column 


248 









100.0 —, 


169 


50.0- 


HERCULES 2400 

DIPHENYLAMINE 


84 


51 


—I—I—r 

M/E 


66 


77 


115 141 

f —| ‘ * 1 I—'—T—|—i—|—i—i—I ‘ I 1 | i—i—i—JfK '— 1 1 t* I—I—I—|—l 

100 120 140 160 



Figure 2b. Mass Spectrum of Scan 298 (Diphenylamine) 


with no degradation. In fact the nitroglycerine 
elutes before the column temperature reaches 100° 
and is only briefly exposed to elevated tempera¬ 
tures in the separator oven. If a standard injector 
is used then the injection temperature must be set 
much lower than normal to avoid decomposition 
of the nitroglycerine. 

An added benefit of the summed spectrum tech¬ 
nique is the elimination of any dependence on 
rigorous reproduction of chromatographic condi¬ 
tions for the tenative identification of smokeless 
powders. The same summed spectrum will result 
from a combination of the same components 
whether the chromatography was performed on a 
capillary or a packed column. In fact, the use of a 
packed column with a high injection temperature 
will result in the decomposition of the nitrogly¬ 
cerine and produce a summed spectrum similar to 
the summed spectrum using our technique and 
subtracting the nitroglycerine contibution. The de¬ 
pendence on chromatography for the creation of a 
summed spectrum could possibly be eliminated 


completely by introduction of the smokeless pow¬ 
der extract by solid probe followed by the summa¬ 
tion and background subtraction steps. 

SUMMARY 

The combination of an on-column injec¬ 
tion/fused silica capillary column/mass spectrom¬ 
eter/data system allows rapid identification and 
comparison of smokeless powders. This technique 
has already been used successfully to compare 
residues from fired cartridge cases with smokeless 
powder deposits found on gunshot victims as well 
as the more routine cases involving IEDs. 

Modification of this technique has numerous 
possibilities in the identification and comparion of 
other items of forensic interest which contain mix¬ 
tures of volatile components or can be pyrolyzed 
to produce volatile compounds such as paints and 
fibers. The mode of ionization is independent of 
the data system techniques involved so chemical 
ionization and negative chemical ionization tech- 


249 
























100 . 0-1 


50.0- 


77 


L.lUl l^U 


92 


I l ‘ < ■ I 


104 


1 UJi 


120 


HERCULES 2400 


ETHYL CENTRALITE 


148 


-i—S—r 


164 


4J. 




268 

I 


t— •—l— 1 —i—'—|—*—r 

250 


1—r 


M/E 


50 


100 


150 


200 


Figure 2c. Mass Spectrum of Scan 392 (Ethly centralite) 


niques may be used to further enhance the speci¬ 
ficity or sensitivity of the detection technique. 

REFERENCES 

Hardy, D. R. and Chera, J. J., (1979), Differ¬ 
entiation Between Single-Base and Dou¬ 
ble-Base Gunpowders, Journal of Forensic 
Sciences, 24, pp. 618-622. 

Mach, M. H., Pallos, A, and Jones, P. F., (1978), 
Feasability of Gunshot Residue Detection Via 
Its Organic Constituents. Part 1: Analysis of 
Smokeless Powders by Combined Gas Chro¬ 
matography-Chemical Ionization Mass Spec¬ 
trometry, Journal of Forensic Sciences, 23pp. 
433-445. 


Meyers, R. E. and Meyers, J. A. (1983), Instru¬ 
mental Techniques Utilized in the Identification 
of Smokeless Powders. Proton Magnetic Re¬ 
sonance (PMR) and Gas Chromatography 
(GC), Abstracts of the International Symposi¬ 
um on Analysis and Detection of Explosives, 
March 29-31, 1983, p. 11. 

Newlon, N. A. and Booker, J. L. (1979), The 
Identification of Smokeless Powders and Their 
Residues by Pyrolysis Gas Chromatography, 
Journal of Forensic Sciences, 24 pp. 87-91. 

Trowel/, J. M. and Philpot, M. C. (1969), Gas 
Chromatographic Determination of Plasticizers 
and Stabilizers in Composite Modified Dou¬ 
ble-Base Propellants, J. Analytical. Chem., 41, 

pp.166-168. 


250 


















Figure 4. Summed spectrum of Hercules 2400 - smokeless powder - Nitroglycerine 


251 



























LIBRARY SEARCH 


Wl 3 2 1 

PUR 968 


SAMPLE 


HERCULES 2400 


O 

Wl 3 10 

PUR 905 


^.—i—I*—,—i . v 

WINCHESTER 473AA 



WINCHESTER452AA 



Figure 5. Library Search of the Summed Spectrum of Hercules 2400 






Figure 6. Library Search of the Summed Spectrum of Hercules 2400-Nitroglycerine 


252 
























































SCAN 

TIME 


Figure 7. Total ion Chromatogram of Norma N-200 



Figure 8. Comparison of the Total ion Chromatograms of Hercules 2400 and Norma N-200 


253 







































100 . 0 -, 


149 


NORMA N—200 


SUMMED SPECTRUM 


50.0- 46 


71 


89 


104 

■ |ll |t i | lji f , i V 1*“ 


169 


210 


i 1 'V ' r*i—|—'—M—i 1 ' —i— 1 i 1 '—| H-i—i—i—i— \ — \ —r 


M/E 


100 150 200 250 

Figure 9. Summed Spectrum of Norma N-200—smokeless powder 


300 



Figure 10. Library Search of the Summed Spectrum of Norma N-200 


254 











































FINGERPRINTS OF DETONATION PRODUCTS FROM NAVY EXPLOSIVES 


J. H. Johnson, E. D. Erickson, C. A. Eleller 
S. R. Smith and L. A. Mathews 
Chemistry Division, Research Department 
Naval Weapons Center, China Lake, CA 93555 

ABSTRACT. The solid products of detonations in nitrogen gas of four Navy ex¬ 
plosives have been collected and analyzed. Although graphs of the products do 
give a rough fingerprint our present examples show too much variation to be of im¬ 
mediate practical use. 


INTRODUCTION 

This work was started at the suggestion of Dr. 
George Young, Naval Surface Weapons Center, 
Dahlgren, Va., as part of the Navy’s Environ¬ 
mental Protection Program. Dr. Young has 
studied the effect of underwater detonations on 
marine life and would like to know what damage 
might be expected from the chemical products of 
the detonation. 

Our initial approach has been to simulate un¬ 
derwater explosions by detonating explosive 
charges in nitrogen gas. By comparison with simi¬ 
lar explosions in air, explosions in nitrogen give 
much more carbonaceous smoke and lower oxida¬ 
tion state gases. There is also less blast effect in ni¬ 
trogen. These features correspond to underwater 
explosions of similar explosives and make our use 
of nitrogen a reasonable initial approach. Even¬ 
tually, underwater tests of some charges will be 
needed to verify the nitrogen work. 

The carbonaceous smoke can be collected, ex¬ 
tracted with organic solvent and the extract ana¬ 
lyzed. This analysis shows several compounds, 
and our initial work with two explosives, TNT and 
PBXN-102, showed different patterns of products 
which conceivably could be used as fingerprints. 
Our continuing work has shown that we are hav¬ 
ing trouble repeating a pattern for an explosive 
from detonation to detonation. We will discuss 
our experiments and plans for sampling/analysis 
which we hope will lead to more consistent results 
for any one explosive. 

EXPERIMENTAL 

Our detonations were carried out in a steel 
walled room with a volume of 38.1 m 3 . The door¬ 


way exits through a labyrinth which has four turns 
and is about 8 m long. Three openings in the ceil¬ 
ing open into stacks that are 3 m high and 48 cm in 
diameter. A steel baffle plate 1 m in diameter and 
7 cm thick protects fans in each of the stacks. For 
our nitrogen tests, the doorway and stacks are 
closed with plywood and polyethylene sheeting. 
Liquid nitrogen is pumped into the room—570 
liters of liquid nitrogen lowers the oxygen content 
below 1% (which is satisfactory judging from our 
results). Unfortunately, the liquid nitrogen also 
cools the walls which may cause condensation of 
part of the product vapors. The explosive charge is 
placed in a Dewar flask to maintain it at ambient 
temperature. We have detonated the explosive 
shown in Table 1. 

Tablet. EXPLOSIVES DETONATED 


TNTC 6 H 3 CH3(N0 2 )3 

Pressed with density = 1.602 g/cm 3 
PBXN 102 
HMX 
A1 

Polymer 


Charges of about 1,600 g are detonated with a 
30 g booster so that the ratio of products will 
strongly favor the main charge. Our gas sampling 
sequence is started just before the detonation so 
that we can measure the amount of oxygen in the 
room atmosphere before the explosion. After the 
detonation, the doorway and ceiling vents are 
open so we have only a short time (30 sec) to col¬ 
lect samples. 

The sampling system has been described in a 
technical paper by J. H. Johnson, E. D. Erick- 


255 




son, S. R. Smith, and C. A. Heller. Products 
From The Detonation of Trinitrotoluene In Air 
And Nitrogen. Naval Weapons Center Technical 
Publication 6420, Nov. 1983. It consists of two 
'/ 2 -inch outer diameter stainless steel tubes going 
through the wall of the room about 75 cm above 
the floor. Gas and particles from the room are 
pumped through both lines and through a filter to 
protect the pump. From these main lines, samples 
can be taken through side lines into evacuated 
flasks or small filters of Tenax, charcoal, Pora- 
pak, or other adsorbants. 

To date, the solids analyses have been done by 
extraction of filters with pentane. A new tech¬ 
nique for thermally desorbing small filters directly 
into the gas chromatograph (GC) should make our 
analysis quicker. The GC peaks are analyzed using 
a Hewlett Packard Model 5985 GC/MS. 

The gas in the flasks is sampled via a T tube 
with a septrum on one arm going into a gas syringe 
and then into a GC which has a thermal conduc¬ 
tivity detector. These samples are described by 
Johnson el al. in his technical paper. 

RESULTS 

Detonations of TNT in air and in nitrogen emit 
very different smoke patterns. Air produces a 
small amount of white smoke while nitrogen pro¬ 
duces a heavy black smoke. Detonations with oxy¬ 
gen varying from 21% down to 0.5% showed a 
sigmoid shaped curve of oxidation of the gaseous 
products. At 21 % oxygen, C0 2 was the only prod¬ 
uct found in the gas samples (water was not meas¬ 
ured). C0 2 begins to decrease when there is about 
15% oxygen and at about 5% oxygen reaches a 
constant value while at the same time a small 
amount of hydrocarbons and a trace of hydrogen 
appears. This lack of change below 5% oxygen 
leads us to think we need not reach 0% oxygen to 
simulate underwater conditions. 

We picture the water explosions to be that of an 
underwater bubble as a fairly self contained gas 
with only small interaction with the water at the 
interface (Figure 1). The gas stays at a high con¬ 
centration and cools slowly. In an ambient temp¬ 
erature gas, the hot gas mixes rapidly with the cool 
gas. This is shown by the fact that in air all the C is 
oxidized to C0 2 . However, the concentration of 
intermediates such as CH 3 , C 2 H 4 and C 2 must re¬ 
main high enough, even in nitrogen, to allow for 
the formation of methane, ethylene and carbona¬ 
ceous particles by bimolecular collisions. An un¬ 
derwater bubble might be expected to provide a 


BUBBLE DIFFUSION 




N 2 ,0 2 mix 

Figure I. Concept of Detonations Underwater and in Air or 
Nitrogen. 

more uniform reaction volume and therefore give 
a more uniform product pattern than does the dif¬ 
fusion mixture in nitrogen. 

Our product patterns from TNT and 
PBXN-102 are shown in the Figures 2-5. We 
show only the larger peaks and have used an ar¬ 
bitrary decision about what the cutoff should be. 
Not even the same list of products shows in pat¬ 
terns from the same explosive. 

One consistency is that unreacted TNT appears 
with the products from TNT detonations. RDX 
and PETN do not appear with their products. 
TNT even appears from detonations in air. This is 
consistent with the large amount of TNT which 
comes out with the black smoke from burning 
TNT. 


DISCUSSION 

The hypothesis that the products of a detona¬ 
tion reaction will depend upon the explosive re¬ 
quires a little discussion (McGuire, 1979). If the 


1900- 

900- 

400- 

200 - 
1 00 - 


1 CYANOBENZENE 

2 METHYLINDENE 

3 NAPHTHALENE 

4 METHYLNAPHTHALENE 

5 METHYLNAPHTHALENE 

A BIPHENYLENE 

6 HC ? 

7 HC ? 

A PHENANTHRENE 

8 HC ? 

9 PHTHALATE ESTER 

10 ADIPATE 

11 PHTHALATE ESTER 



1 23 4 5 a6 7a8 91011 

Figure 2. Detonation Products from PBXN-102 in Nitrogen 
on Quartz Wool (E43). 


256 



















naphthalene 



Figure 3. Detonation Products from PBXN-102 in Nitrogen 
on Tenax (E41). Product Numbers are the Same as Listed in 
Figure 2. 


explosive breaks down to atoms which then reas¬ 
semble to molecules and carbonaceous particles, 
the products would depend upon the atomic com¬ 
position, temperature, pressure. Then, any two 
explosives with the same atomic composition and 


1 ALKANE 

2 ALKANE 

3 ALKANE 

4 ALKANE 

5 CYANOBENZENE 


7 ALKANE 

8 ALKANE 

9 ALKANE 

A METHYLCYANOBENZENE 

10 ALKANE 

11 ALKENE 

12 ALKENE 

13 ALKANE 

14 NAPHTHALENE 

15 METHYLNAPHTHALENE 

16 METHYLNAPHTHALENE 

A NITROBENZENE 

B DNT 

17 TNT 

18 PHTHALATE ESTERS 

19 X 

20 X 

21 X 

A ALKANE 

B DI OCTYL ADIPATE 

22 PHTHALATE 

23 ALKANE 


(6430) 


tnt 

l 


q 



Figure 4. Detonation Products of Pressed TNT in Nitrogen on 
Tenax (E38). 



Figure 5. Detonation Products of Pressed TNT in Nitrogen on 
Tenax (E39). Component Numbers are the Same as Those 
Listed in Figure 4. 


equal energy would give intermediate atomic 
mixes which would then combine to give the same 
fingerprint of the product. That is, a given pro¬ 
duct fingerprint could come from different orig¬ 
inal explosives. 

A more likely picture would be that a portion of 
the molecules don’t break down to atoms in the 
detonation, but retain some of their structure. 
Then, the recombination of atoms and atomic 
groups might give rise to a few large molecules 
whose composition would depend upon the orig¬ 
inal explosive’s molecular composition. These 
large molecules would be found condensed on the 
carbonaceous particles on chamber walls or in wa¬ 
ter for an underwater detonation. The discovery 
of unreacted TNT in our experiments shows that 
large “fragments” can survive detonations under 
some conditions. Others at this conference 
(Sharma, 1983) have reported similar findings in¬ 
cluding monomolecular coatings on pipe bomb 
casings. On the other hand, one would expect few¬ 
er molecular remnants for confined explosives 
than for our unconfined tests. 

Real underwater detonations of confined explo¬ 
sives should form a good test of the atomic recom¬ 
bination hypothesis. The original confined mole¬ 
cules might be expected to break down completely 
to atoms. Then, the underwater bubble would 
form a uniform, reproducible reaction chamber 
where atoms could recombine to form a pattern of 
molecules. 

To date, our work has proven nothing about 
product fingerprints. We have shown that some 
molecules survive the detonation. We have found 
some large molecules we think are from the explo¬ 
sive. Our sampling system has needed improve¬ 
ments and these are being made. We shall con¬ 
tinue to study how much carbonaceous product is 


257 



































































formed and how large a burden of toxic chemicals 
are carried on these particles. However, we will al¬ 
so examine the fingerprints as we continue. 


REFERENCES 

R. R. McGuire, D. L. Ornel/as and /. B. 

Prop, and Explo., 4, 23-26 (1979). 
Sharma, J. Presentation #21 at this meeting. 


Akii. 


258 


THE ANALYSIS OF TRACE LEVELS OF EXPLOSIVE BY 
GAS CHROMATOGRAPHY/MASS SPECTROMETRY 


A. S. Cumming and K. P. Park 
EM2 Branch 
RARDE 

Royal Arsenal East 
Woolwich 
London SE18 6TE 


ABSTRACT. The identification of trace levels of explosive is a problem faced by 
forensic analysis. In principle the Mass Spectrometer is a very powerful tool for use 
in these analyses, since considerable structural information can be obtained from 
the mass spectrum. However, when dealing with explosives in a conventional Mass 
Spectrometer major problems are experienced due to the extensive fragmentation, 
particularly with the non-aromatic nitrate esters and nitrocompounds such as ni¬ 
troglycerine and RDX. Much use can, however, be made of this limited informa¬ 
tion by the use of a high efficiency capillary Gas Chromatograph coupled to the 
Mass Spectrometer. Some of the problems will be described and the detection lim¬ 
its possible with Single Ion Monitoring of the most abundant ion (typically in the 
low nanogram range) will be discussed. Other forms of ionisation are possible, 
however, and the application of the negative ion mode will be described. This tech¬ 
nique is particularly appropriate to the analysis of explosives, since electron cap¬ 
ture is the principal mechanism of ionisation, and common explosives are strongly 
electron capturing, a property made use of in their Gas Chromatographic analysis. 
Not only does the negative ion mode produce improved detection limits, but also 
introduces a degree of discrimination not available in conventional Mass Spec¬ 
trometry. The implications of these newer developments in Mass Spectrometry for 
the analysis of explosives traces will be discussed. 


INTRODUCTION 

Mass Spectrometry is generally considered to be 
one of the most powerful tools available to the 
analytical chemist for the characterisation of an 
unknown material. A review of its application 
within the field of explosives analysis has ap¬ 
peared (1). However, the analysis of explosives by 
conventional mass spectrometry presents prob¬ 
lems. Ionisation by electron impact (El), in which 
the sample is bombarded by electrons at 70eV in 
high vacuum, produces substantial fragmentation 
of most explosive molecules and hence oversimpli¬ 
fied spectra whose usefulness as a means of identi¬ 
fication is limited. 

This limited usefulness arises from the poor 
charge stabilising properties of the nitro group. 
Molecular ions of nitro-alkanes eject the nitro 
group so readily that a molecular ion (M + ) is sel¬ 
dom observed. Under the standard El condition 


of 70eV and high vacuum none of the nitrate es¬ 
ters gives a molecular ion. The major peaks which 
occur at 30, 46 and 76 mass units are due to frag¬ 
ments identified as: 

NO + (30), NO 2 + (46), (H 2 C-0-N02) + (76). 

In contrast aromatic nitro compounds do give 
molecular ion peaks and are thus more amenable 
to study in El. The fragmentation of TNT has 
been studied in detail (11) and it has been shown 
that the Base Peak at m/z 210 corresponds to 
(C7H4N3O5) + which corresponds to the loss of 
OH from the molecular ion. 

In order to make the best possible use of this 
limited means of characterisation, it is essential to 
achieve an efficient separation of mixtures prior to 
ionisation. This is commonly done by attaching a 
Gas Chromatograph to the Mass Spectrometer 
(GC/MS). The method may be employed with 
packed, borosilicate capillary or fused silica capil- 


259 


lary columns. Fortunately most of the explosives 
regularly encountered are sufficiently volatile to 
be amenable to gas chromatographic analysis. 

Although El mass spectrometry has been the 
standard technique for many years, mass spec¬ 
trometry is applicable to both positive and nega¬ 
tive ions. Because of the greater ease with which 
reproducible El spectra may be obtained from 
most molecules the study of negative ion spectra 
has been neglected until recently (2,3). The revived 
interest is due to improvements in both ionisation 
techniques and instrumentation, allowing ma¬ 
chines designed primarily for positive ion opera¬ 
tion to be easily adapted to produce and detect 
negative ions. 

For an explosives analyst the attraction of nega¬ 
tive ion (NI) spectrometry lies in its selectivity. 
Under appropriate conditions the predominating 
mechanism of ion production is electron capture, 
behaving in the same fashion as the gas chromato¬ 
graphic electron capture detector, one of the most 
sensitive explosives detectors available. It has been 
shown that the spectra depend on a large number 
of variables (2,3,4), e.g. temperature, pressure, 
ionisation energy. The three distinct mechanisms 
by which negative ions can be formed, each of 
which is dependent on electron energy are: 

(a) Resonance Capture. 

AB -l- e ( + M) -*■ AB: ( + M) (energy 

0-10eV) 

(b) Dissociative resonance capture. 

AB + e — A- + B. (0-15eV) 

(c) Ion pair formation. 

AB + e-*-A + B- -I- e(10eV) 
where AB is the species under examination; e is an 
electron, and M is a moderator species. 

Due to the low energy required to produce reso¬ 
nance capture the presence of a moderator or buf¬ 
fer gas (M) is necessary to maximise the process in 
a conventional mass spectrometer source. A pres¬ 
sure of approximately 1.33 kPa is required. This 
moderator, usually a gas such as methane or nitro¬ 
gen enhances the formation of low energy elec¬ 
trons (0-10eV) which are then captured by the 
sample. At low pressures the other two mecha¬ 
nisms (b and c) predominate. These are intrinsical¬ 
ly inefficient methods for the production of nega¬ 
tive ions giving rise to radical or positive ionic 
spectra and extensive fragmentation. 

At high pressure (2.66-3.99 kPa) fragmentation 
can be practically eliminated, producing spectra 
analogous to those observed under positive ion 
chemical ionisation conditions (Cl). At these pres¬ 


sures additional reactions take place within the ion 
source (1). 

The work described here was undertaken to in¬ 
vestigate the sensitivity of the VG 16F in positive 
and negative mode as a means of identifying traces 
of explosive. It was thought that a combination of 
the two techniques would prove of considerable 
use in GC/MS analyses. Low pressure NI-MS us¬ 
ing methane as a moderator was studied as it was 
considered that acquiring the additional informa¬ 
tion from fragmentation of the sample molecules 
would be an advantage. High pressure NI-CI 
mass spectrometry was not studied at this stage. 
Recently, however, some reports of its application 
to the analysis of nitrate esters within the bio¬ 
chemical field have appeared (5,6,7). These stud¬ 
ies indicate the high sensitivities possible, with 
picogram detection limits reported. 

EXPERIMENTAL 

All mass spectra were obtained on a VG Organ¬ 
ic 16F single focussing magnetic sector instru¬ 
ment. The schematic layout is shown in Figure 1. 
It is equipped with packed and capillary column 
gas chromatographic inlets. The packed column 
inlet is equipped with a jet separator to remove ex¬ 
cess carrier gas. 

The mass spectrometer has been modified using 
a set of standard units supplied by VG Analytical 
to enable negative ion spectra to be obtained. This 
equipment enables the polarity of the accelerating 
voltage and the ion beam focussing controls to be 
reversed (-4kV to + 4kV). The polarity of the 
electromagnet was also reversed, but the electron 
multiplier was maintained at -2kV, the momen¬ 
tum of the ions in the flight tube being sufficient 
to overcome the deceleration produced. 

For the study of negative ion spectra methane 
was introduced into the source via an inlet system 



Figure 1. Schematic Layout of a Mass Spectrometer 


260 




controlled by pressure equalisation valves, thus 
ensuring a steady supply of gas to the source. This 
system was designed for use in chemical ionisation 
studies but is equally applicable to negative ion 
work. A pressure in the source housing of 2.66 x 
lCr ? kPa was used giving an approximate pressure 
of 0.6-2 kPa within the partially sealed source. 

The source conditions used for both positive 
and negative ion studies are respectively Emission 
current, 200 and 500 uA; Electron Energy, 70eV 
for both. 

The chromatographic materials used were: 

Packed column 2m 3% OV17 on Chromo- 
sorb W(HP) 80-100 mesh. Flow 20 ml 
min' 1 He. 

Borosilicate Capillary 12.5 m x 0.5 mm id. 
WCOT OV17. Flow between 1 & 3 ml 
min -1 He. 

Fused Silica Capillary. 12.5 m x 0.2 mm id. 
Methyl Silicone. Flow rate approx 1 ml 
min' 1 He. 

The samples used were obtained from pure ref¬ 
erence collections and are listed below: 

Ethylene glycol dinitrate: EGDN 

Nitroglycerine: NG 

Tetramethoxymethane tetranitrate: PETN 

1.3.5- trinitro-l ,3,5-triazacyclohexane: 
RDX 

2.4.6- trinitrotoluene: TNT 

Single Ion Monitoring (SIM) of the most abun¬ 
dant ion was used to determine the detection limit. 





Prior to attempting GC sensitivity experiments 
samples of pure explosives were examined to ob¬ 
tain reference spectra. The positive and negative 
ion spectra are shown in Figures 2-6. 


- 100 % 


PETN POSITIVE ION 


iLiiL—.. 1. 


- 100 % 



METHANE ENHANCED 
NEGATIVE ION 


il. ... lu 


Figure 4 


261 





























100 


- 100 °/. 



2,4,6 TNT 

POSITIVE 

ION 



A standard sample volume of 0.2 ul was used 
for all capillary work, and splitless injection was 
employed, thus allowing direct injection of small 
amounts. 

The sensitivity to a given explosive depends on 
the percentage of the total sample which is present 
in the mass spectrum as the ion whose intensity is 
being monitored. Molecules which are totally ion¬ 
ised to give a single species, whether a molecular 
ion or not will give a better detection limit than 
molecules which undergo- extensive fragmenta¬ 
tion. With most of the explosives examined the 
second situation is experimentally observed, and 



thus the sensitivity is lowered. Because the frag¬ 
ment at m/z = 210 is relative stable, TNT under¬ 
goes less complete fragmentation and this contrib¬ 
utes to its low detection limit compared with that 
of NG. 

It is apparent that the overall sensitivity of the 
spectrometer is far greater using capillary columns 
than with the packed column, and that fused silica 
columns offer an increase in sensitivity over boro- 
silicate columns. The reasons for this are various. 
The 60-70% efficiency of the jet separator essen¬ 
tial for packed column operation accounts for 
some loss in sensitivity, but more important are 


RESULTS AND DISCUSSION 

Detection Limits for Positive Ion Operation. 


Explosive 

Sim Ion 

Packed Column 

Borosilicate Capillary 

Fused Silica 





Capillary 

EGDN 

46 

100 ng 

1 ng 

250 pg 

NG 

46 

100 ng 

10 ng 

1 ng 

PETN 

46 

100 ng 

25 ng 

10 ng 

RDX 

46 

500 ng 

200 ng 

30 ng 

TNT 

210 

5 ng 

520 pg 

50 pg 

Capillary Chromatographic Conditions for Positive Ion. 



Explosive 

Manifold Temp (°C) 

Injector Temp (°C) 

Oven Temp (°C) 

Source Temp (°C) 

EGDN 

150 

125 

90-165* 

150 

NG 

150 

125 

90-165* 

150 

PETN 

150 

125 

90-165* 

150 

RDX 

200 

200 

200 

200 

TNT 

250 

250 

210 

200 


♦TEMPERATURE PROGRAM-Initial Temp: 1 min; Temp Ramp: 3°Cmin 1 ; Final Temp 10 mins. 


262 



































SEPTUM 

PURGE 




Figure 7 


the opportunities for sample loss within the col¬ 
umn. This may be minimised by the use of all glass 
equipment since nitrate esters in particular readily 
decompose in contact with hot metal. This de¬ 
composition may be further reduced by removing 
all active sites. Due to impurities within most com¬ 
mon glasses a substantial number of these active 
sites are present on the accessible surfaces of both 
the packed and borosilicate capillary columns. 
Fused silica contains far fewer active sites of this 
kind and therefore the detection limit for suscepti¬ 
ble materials is lower. In addition the flexibility of 
the fused silica column permits direct connection 


to the mass spectrometer source, avoiding the use 
of lengths of connecting tubing, (Figure 7). 

Experience has shown that the performance of 
fused silica columns does tend to deteriorate with 
time, probably due to column bleed rendering ac¬ 
tive sites on the column wall accessible. This effect 
should be minimised by using bonded phases, the 
application of which is currently under evaluation. 

The detection limits for negative ion GC/MS of 
explosives were determined solely with fused silica 
capillary columns, because of the greater sensitiv¬ 
ity achieved with them in El mode. The limits ob¬ 
tained are shown below. 


DETECTION LIMITS FOR NEGATIVE ION GC/MS OF EXPLOSIVES. 


Explosive 

Sim Ion 

Detection Limit 



EGDN 

62 

250 pg 



NG 

62 

1 ng 



PETN 

62 

10 ng 



RDX 

46 

30 ng 



TNT 

210 

125 pg 



G C Conditions for Negative Ion GC/MS. 




Explosive 

Manifold Temp (°C) 

Injector Temp (°C) 

Oven Temp (°C) 

Source Temp (°C) 

EGDN 

150 

150 

100 

160 

NG 

150 

150 

145 

160 

PETN 

150 

150 

155 

180 

RDX 

200 

250 

190 

200 

TNT 

250 

250 

230 

200 


It is clear that NI-MS is likely to have a major 
impact on the use of mass spectrometry in the de¬ 
tection and identification of traces of explosives. 
In operation the ionisation processes are compara¬ 


ble to those in the Electron Capture Detector 
which has become essential in the GC analysis of 
explosives for reasons of both sensitivity and se¬ 
lectivity. This means that it is possible to operate 


263 




































at high sensitivity in the present of considerable 
amounts of non-electron capturing solvent. 
Solvent creates a major problem in El were 
solvent tails can prevent confirmation of the pres¬ 
ence of explosives. Similarly the presence of 
non-electron capturing impurities in the sample 
will cause far fewer problems than can be expe¬ 
rienced in El. 

The spectra themselves are relatively simple, 
and provide evidence additional to that furnished 
by El. Under the conditions produced by a low 
pressure of moderator gas there is often insuffi¬ 
cient evidence to characterise the explosive using 
NI-MS alone. However, the combination of NI, 
El and a GC retention time provides very strong 
evidence indeed for identifying the species. For ex¬ 
ample in the case of NG: SIM at 46 mass units in 
NI and El; SIM at 62 mass units in NI and a reten¬ 
tion time corresponding to that of NG indicates 
the presence of an electron capturing compound 
containing species which give rise to (a) N0 2 (46); 
(b) N0 2 + (46); (c) N0 3 “ (62). Apart from nitroben¬ 
zene (NB) (Figure 8), only nitrate esters give rise to 
appreciable amounts of N0 3 , and NB can be 
eliminated by a study of the ratio of N0 3 ~ to 
N0 2 “ which is close to 2 for nitrate esters and 
close to 0.5 for nitrobenzene. In addition the mo¬ 
lecular ion peak for NB is of approximately the 
same intensity as the N0 3 ~ peak. These two fac¬ 
tors provide enough information to eliminate NB. 
Therefore using the SIM information it is possible 
to identify a nitrate ester by comparing its reten¬ 
tion time with that of a known standard, e.g. NG. 
This gives very convincing evidence of identity. 
Further evidence would depend on the sample 
amount, since below a level generally an order of 
magnitude greater than the detection limit, it is 
impossible to obtain a complete spectrum. The 
work carried out so far indicates that the detection 
limits obtainable in practice for NI are of the same 
order as for El. This is not as good as might be ex¬ 
pected, since it has been suggested that sensitivities 
at least an order of magnitude greater should be 
obtainable for NI (Reference 8). The explanation 
for this probably lies in the compromises made in 
modifying the 16F to obtain negative ion spectra. 
A dedicated instrument would be capable of a 
much closer approach to the theoretical sensitivi¬ 
ties. In addition the conditions used for this study 
may not be optimum. The pressure of moderator 
gas employed may not be producing the optimum 
mean free path for negative ion production, and 
this together with a 2kV deceleration at the collec- 


100 % 


NITROBENZENE 

NEGATIVE ION 


J Li . i. 


Figure 8 


tor will drastically lower the efficiency of the sys¬ 
tem. Some further work on moderator gas pres¬ 
sure will be necessary to resolve this point. It is 
worth nothing that the spectra of explosives ob¬ 
tained with methane differ somewhat from those 
obtained in nearly identical conditions with isobu¬ 
tane (Reference 9). 

Methane at the pressure employed does not pre¬ 
vent fragmentation of the molecular ion. In order 
to increase the sensitivity and indeed the selectiv¬ 
ity, this fragmentation should be minimised, 
which would result in a greater intensity of the 
molecular ion. However, fragmentation can be 
useful in providing additional evidence of the 
identify of the sample, e.g. distinguishing the 
DNT isomers. It has been reported that chlori¬ 
nated species, such as CHC1 3 enhance the molecu¬ 
lar ion by the formation of ion clusters (Reference 
10). It may be possible to approach the suggested 
sensitivity of NI by making use of gases such as 
CHC1 3 and NH 3 in the low pressure mode. This 
may stabilise the molecular ion to some extent, 
though full stabilisation is not likely without op¬ 
erating at high pressure, i.e. NI-CI. Further work 
will be undertaken to confirm whether this behav¬ 
iour is observable with the present instrument. 
The fragmentation observed with methane as the 
moderator is not identical to that observed in El. 
As yet the routes are not well documented, But a 
notable feature is the formation of N0 3 “ (62 mass 
units) as the base peak in the nitrate esters, 
EGDN, NG and PETN. Since, apart from NB, the 
other nitrocompounds studied do not give this 
ion, and since NB is readily distinguishable, this 
provides a means of identifying nitrate esters. 
Both nitrocompounds and nitrate esters give 
N0 2 ~ (46 mass units). As N0 2 + this forms the 
base peak observed in El for nitrate esters and 
non-aromatic nitrocompounds. 

The detection limit of TNT in the negative mode 


264 






is somewhat higher than in El. The use of 210 
mass units for SIM for both NI and El detection 
limits means that the sensitivity depends on the 
proportion of the total ion current that reaches the 
collector as the ion of mass 210. The negative ion 
spectrum of TNT has a much enhanced molecular 
ion with a corresponding decrease in the sensi¬ 
tivity when 210 mass units (which remains the base 
peak) is used for single ion monitoring. The base 
peak of 210 indicates that the loss of OH • is still a 
major feature of the fragmentation of TNT, but 
that the molecular ion is much more stable. 

Further fragmentation in TNT does take place, 
but apart from a major peak at 197 mass units, as¬ 
signed as C 7 H 5 N 2 05 “ (Reference 1), which also 
takes an appreciable proportion of the total ion 
current, it is at a low level. This pattern of frag¬ 
mentation suggests that under the correct condi¬ 
tions the fragmentation could be completely elimi¬ 
nated, leading to the use of 227 for single ion 
monitoring and greatly enhanced sensitivity. 

The identity of the various fragment ions re¬ 
mains to be determined for most of the explosives 
studied. Such identification would require consid¬ 
erable work, including accurate mass determina¬ 
tions and possible isotopic substitution. However, 
the lack of such data does not preclude the use of 
NI as an analytical method of great value and of 
negative ion spectra as a ‘fingerprint’ characteris¬ 
tic of a compound. 

CONCLUSIONS 

The combination of El, NI, and high perform¬ 
ance capillary chromatography provides a very 
powerful analytical system capable of giving a 


clear positive identification of explosives material 
at minimum levels between 100-150 ng, depending 
on the explosive, at which levels a complete mass 
spectrum may be obtained. Using Single Ion or 
Multiple Ion Monitoring of the most abundant 
peaks a very high degree of confidence of identifi¬ 
cation is possible at picogram levels. 

REFERENCES 

1. Yinon J., Zitrin S. The Analysis of Explo¬ 
sives: Pergamon Press (Oxford) 1981. 

2. Busch K L. Ph D Thesis, University of N. 
Carolina 1979. 

3. Hunt D. F., Crow F. W. Trace Organic 
Analysis. A New Frontier in Analytical. 
Chemistry, NBS 9th Materials Research Sym. 
Proc 1978. 

4. Jennings K R. Phil Trans R. Soc. Lond. A293 
125 1979. 

5. Gen’ich Idzu et al. J Chromatog, Biomed. 
Appl. 229, 327 1982. 

6. Bignall J C et al. Anal Chem. Symp. Series 
Vol. 7. Elsevier (Amsterdam) 1981. 

7. Horning E C et al. J Chromatog Lib 20 359 
1981. 

8. Hunt D F et al. Anal Chem 48 (14) 2098. 
1976. 

9. Yinon J . J Forensic Sci 25 (2) 401, 1980. 

10. Bouma W. J., Jennings K. R. Org. Mass 
Spect. 16 (8) 331, 1981. 

11. Bulusu S., Axenrod T. Org. Mass Spect. 14 
(1 1) 585; 1979. 

Copyright: © Controller, Her Majesty’s Station¬ 
ery Office, London 1983. 


265 




































ANALYSIS OF EXPLOSIVES AND EXPLOSIVE RESIDUES 
WITH ION MOBILITY SPECTROMETRY (IMS) 


G. E. Spangler, J. P. Carrico, S. H. Kim 
The Bendix Corporation 

Environmental and Process Instruments Division 
1400 Taylor Avenue 
Baltimore, Maryland 21204 


Abstract. The detection and analysis of explosives using Ion Mobility Spectrom¬ 
etry (IMS) is described. Results for trinitrotoluene (TNT), dynamite, cyclonite 
(RDX), and composition B (TNT/RDX) are presented. Methods by which sample 
can be introduced into IMS are discussed. These include ambient air carrier gas, 
sample wire probe/syringe, solids probe, desorption oven, membrane inlet, expo¬ 
nential dilution flask, standards generator, surface sampler, and gas chromato¬ 
graphy. A compact IMS system is described which has obvious application as an 
explosive vapor detector. 


INTRODUCTION 

A problem of significant interest to forensic 
science is the detection of explosives and explo¬ 
sives residues either before or after a detonation 
incident. A variety of techniques have been con¬ 
sidered for this application including high pressure 
liquid chromatography, thin layer paper chroma¬ 
tography, gas chromatography using electron cap¬ 
ture or photoionization detectors, ion chroma¬ 
tography, mass spectrometry, NO x chemilumines¬ 
cence, light miscroscopy and X-ray photoelectron 
spectroscopy. This paper describes another tech¬ 
nique known as Ion Mobility Spectrometry (IMS). 
With proper sampling techniques, IMS can be 
used to analyze and detect explosives in the vapor, 
liquid or solid phase with basic sensitivities ap¬ 
proaching one part in 10" or 1 picogram (Spangler 
and Lawless 1978, Karasek 1974). Because IMS 
works under atmospheric pressure conditions, it 
avoids excessive hardware encountered with vac¬ 
uum technology and can be miniaturized into a 
compact detector alarm system for field use (Car¬ 
rico, et al. 1982). 

ION MOBILITY SPECTROMETRY 
The Technique 

Figure 1 illustrates the technique of IMS. IMS 
consists of a cell in which there exists two re¬ 
gions: (1) the reaction region and (2) the drift re¬ 
gion. In the reaction region, a carrier gas flows 


whose composition is typically purified air (i.e. air 
with less than parts per million of water and less 
than parts per billion of ammonia, NO x , and halo- 
genated compounds). A Ni-63 radioactive source 
ionizes the carrier gas to produce what are called 
reactant ions. When sample is introduced into the 
carrier gas, the reactant ions undergo ion/mole¬ 
cule reactions with the sample to produce product 
ions. Under the influence of an electric field, the 
mixture of ions are drawn to a shutter grid where 
they are introduced into the drift region. The shut¬ 
ter grid is pulsed “on” and “off” periodically to 
introduce small amounts of ions into the drift re¬ 
gion. 

Once in the drift region, an electric field draws 
the ions to a collector (Faraday Plate) where they 
are collected as pulses of ion current separated by 
arrival times of ions. These pulses are amplified by 
an electrometer circuit and sensed by an oscillo¬ 
scope, signal averager, or microprocessor. Coun- 


GAS 

EXIT 



Figure 1. Ion Mobility Spectrometer. 


267 
















terflowing in the drift region is a clean drift gas, 
entering near the collector and exiting near the 
shutter grid, which quenches reactions that con¬ 
tinue in the drift region and distort the symmetry 
of the ion mobility peaks. The successful use of 
IMS requires exercising proper control on the 
composition and purity of the carrier and drift 
gases. 

In simplest terms, IMS can be thought of as an 
Atmospheric Pressure Ionization (API) source 
coupled to an ion mobility drift tube. It is thus a 
cousin to Atmospheric Pressure Ionization Mass 
Spectrometry (API/MS). 

IMS is further illustrated in Figure 2. The vari¬ 
ous ions (A, B and C) formed in the reactor are 
pulsed by the shutter grid into the drift region 
where they are separated (C, B and A) into ion 
mobility peaks (A, B and C). The separation oc¬ 
curs as the result of differences in the drift veloci¬ 
ties for the various ions. 

The theoretical relationships for the drift veloc¬ 
ity are shown in Figure 3. The drift velocity is pro¬ 
portional to the electric field through a scalar 
parameter, K, known as mobility. Since the drift 
velocity is the drift length, d, divided by the drift 
time, t d , of the ion to the collector, the mobility is 
the drift length divided by the drift time and elec¬ 
tric field. That is, the mobility is inversely propor¬ 
tional to the drift time of the ion. 

The mobility of gaseous ions in weak electric 
fields has been studied by Mason and Schamp 
(Mason and Schamp 1958, 1972). According to 
the core model of these authors, the mobility is in¬ 
versely proportional to the collision cross section 
of the ion, Trr^Q 0,1 **, and the neutral gas density N 
as shown in Figure 4. To remove the effects of 
variable gas density, mobility can be normalized 
against temperature and pressure as shown in Fig¬ 
ure 3. The result is reduced mobility. Reduced mo- 


DRIFT VELOCITY (V d ) 
V d = KE 

MOBILITY (K) 



REDUCED MOBILITY (K Q ) 

K - K _P_ . 213 
0 760 T 

Figure 3. Relationship between Ion Velocity and Mobility. 

bility is empirically related to the mass of the ion 
with larger ions having longer drift times and 
smaller ions having shorter drift times. However, 
because the correlation between drift time and 
mass is rough, IMS must be considered at best as a 
poor man’s mass spectrometer. Ion mass informa¬ 
tion can only be obtained from IMS coupled to a 
mass spectrometer. 

The Ion Mobility Spectrometer/Mass Spec¬ 
trometer (IMS/MS) system at Bendix is shown in 
Figure 5. The system consists of a Bendix stacked 
ring IMS coupled to an Extranuclear SPECTREL 
mass spectrometer. The mass spectrometer is con¬ 
figured to accept an atmospheric pressure ioniza- 


I0NIZER 


—— ELECTRIC FIELD —► 



A n 

DRIFT REGION 




c 

B 

A 



B n 






8 c" 

c 

B 

A 



Afl r. 


B 









CA U 






8 n 

C 

B 

A 



AA U 

A8 n 

C 

B 

A 



ccU 

C 

B 

A 



SHUTTER 

GRID 


COLLECTOR 



MASON-SCHAMP THEORY FOR MOBILITY 


K 


3 e f J_ + Jj 1/2 

16 N [ in M J 


2 


k 




_♦_A__ 

ft* 1 ' 11 ' 


WHERE 

e = IONIC CHARGE 

m » IONIC MASS 

N = MOLECULAR NUMBER DENSITY 

M = MOLECULAR MASS 

k = BOLTZMANN CONSTANT 

T = TEMPERATURE 

r m = POSITION OF MINIMUM POTENTIAL FOR INTERACTION 
= FIRST ORDER COLLISON INTEGRAL 
A * CORRECTION TERM FOR HIGHER APPROXIMATIONS 


Figure 2. Ion Motion in Ion Mobility Spectrometry. 


Figure 4. Mason-Schamp Theory for Mobility. 


268 






















Figure 5. Ion Mobility Spectrometer/Mass Spectrometer System at Bendix. 


tion source. The schematic layout of the system is 
shown in Figure 6. Provided in the collector of the 
IMS is a hole to allow passage of ions from the 
IMS to the MS. A potential is applied between the 
collector of the IMS and the 25 micron ion aper¬ 
ture into the high vacuum region of the MS. The 
ions pass from the IMS, through the collector, 
through the pinhole and into the API focusing 
lenses of the mass spectrometer. Two stage pump¬ 
ing is provided with a turbomolecular pump evac¬ 
uating the inlet or ion optic section and diffusion 
pumps evacuating the analyzer or quadrupole fil¬ 
ter section of the mass spectrometer. 

Four types of data are available from IMS/MS 
as shown in Figure 7. The first is the ion mobility 
spectrum collected from the IMS. The second is 
the total ion mass spectrum collected with the 
shutter grid of the IMS open so that all ions gener¬ 
ated in the IMS can be analyzed by the mass spec¬ 
trometer. The third is the ion mobility spectrum 


collected through the mass spectrometer operated 
in its total ion mode (dc voltage zero). The fourth 
is the mass identified mobility spectrum which is 
the ion mobility spectrum collected through the 
mass spectrometer tuned to a specific mass. Ex¬ 
perimentally, ion mobility spectra are first col¬ 
lected from the IMS to obtain reduced mobility in¬ 
formation. To correlate the ion mobility peaks 
with ion masses, this spectrum is then compared to 
the same spectrum collected through the mass 
spectrometer. By tuning the mass spectrometer to 
ions observed in the total ion (or API) mass spec¬ 
trum, ion masses are correlated with ion mobility 
peaks via mass identified mobility data. 

Ion Mobility Spectra for Explosives 

Using IMS with a membrane inlet (Spangler, 
Suh, and Carrico 1980, Spangler and Carrico 
1983), IMS signatures were collected on head 
space vapors from various explosives. The oper- 


269 











ION MOBILITY w L ion focussing 
SPECTROMETER - *!*" GAS JET 

SEPARATION 



QUADRUPOLE 

MASS 

SPECTROMETER 



FARADAY FOCUSSING QUADRUPOLE CHANNELTRON 

PLATE LENSES RODS ELECTRON 




760 TORR 



10~ 4 TORR 



10 5 


TO I0 6 


TORR 



Figure 6. Schematic of Ion Mobility Spectrometer/Mass Spectrometer System. 


8200I-55B 


ating parameters for the IMS instrument are 
shown in Table 1. The drift housing temperature 
was 200°C, drift gas temperature was 106— 
112°C*, inlet temperature was 227°C, the sample 
gas was ambient air, and the carrier and drift gases 
were purified air (approx. 4 ppm water or less) as 
generated by an AADCO Pure Air Generator. 


Table 1. OPERATING PARAMETERS USED FOR THE 
ANALYSIS OF EXPLOSIVES WITH ION MO¬ 
BILITY SPECTROMETRY 


Ion Mobility Spectrometer 

CARRIER GAS 
DRIFT GAS 
SAMPLE GAS 
MEMBRANE 
DRIFT FIELD 
DRIFT HOUSING 
TEMPERATURE 
DRIFT GAS 
TEMPERATURE 
INLET TEMPERATURE 
SAMPLE 
GENERATION 

TEMPERATURE 


PURIFIED AIR 
PURIFIED AIR 
AMBIENT AIR 
DIMETHYLSILICONE 
197 VOLT/CM 
200 °C 

106- 112°C 

227 °C 

SATURATED VAPOR 

PRESSURE 

AMBIENT 


The negative ion spectra for various explosives 
are shown in Figure 8. The top spectrum is the 
normal reactant ions (CT or C0 3 “ clustered with 
water). The other spectra are product ion spectra 
from which has been subtracted the reactant ions. 
The reactant ions are negative going peaks and the 
product ions are positive going peaks for these 
data. The results for composition B shown contri¬ 
butions from dinitrotoluene (DNT) and trinitroto¬ 
luene (TNT) but not cyclonite (RDX). RDX does 
not contribute to the composition B data because 
of the involatility of RDX in the vapor phase. The 
RDX results were obtained by flash evaporating 
RDX dust deposited on a solid sample probe in¬ 
serted into the inlet. The spectrum for dynamite 
was obtained by sampling head space vapors. A 


- ION MOBILITY SPECTRUM 

- TOTAL ION MASS SPECTRUM 

- TOTAL ION MOBILITY SPECTRUM 

- MASS IDENTIFIED MOBILITY SPECTRUM 


* Drift gas temperature is less than the drift housing tem¬ 
perature because drift gas was not preheated. 


Figure 7. Types of Data Obtained from Ion Mobility Spec¬ 
trometer/Mass Spectrometry. 


270 































































more detailed discussion of these spectra will now 
follow. 

Beginning with dynamite, the 2.10 cm 2 V -1 s _1 
peak is not due to the explosive itself but rather to 
impurities of low electron affinity, (Spangler, Car¬ 
rico and Campbell 1983). The peak of significance 
is the ion with reduced mobility 2.48 cm 2 V” 1 s _l . 
This ion lies close to the reactant ion mobility peak 
(reduced mobility 2.57 cm 2 V -1 s _1 ) and cannot be 
resolved from the reactant ion without reactant 
ion subtraction. A similar ion has been observed 
by other authors (Asselin 1978 and Wernlund, 
Cohen and Kindel 1978) with Wernlund, et at. 
identifying the ion as NO/ from IMS/MS data. 
The reactions leading to the formation of the NO/ 
are displayed in Figure 9. The NOf ion may come 
from the nitroglycerin itself or from ethylene gly¬ 
col dinitrate, an impurity in dynamite. As the tem¬ 
perature of the IMS is decreased, Figure 10 shows 
that the 2.48 cm 2 V~ 1 s" 1 peak for dynamite disap¬ 
pears in favor of the 1.37 cm 2 V _I s _1 peak (Wern¬ 
lund, Cohen and Kindel 1978 and Spangler 1978). 
The 1.54 cm 2 V -1 s -1 ion mobility peak for TNT is 
shown for reference in this figure. IMS/MS data 
show that the 1.37 cm 2 V -1 s -1 peak is nitroglyc¬ 
erin clustered with N0 3 “ (Wernlund, Cohen and 
Kindel 1978). This result is consistent with the 
interpretation that ion attached moieties are more 
stable at reduced temperature because either the 
neutral molecule is more stable or the cluster is 
more stable. Wernlund, Cohen and Kindel showed 
that nitrate compounds dissociate easier as the 
number of nitrate groups increases (Wernlund, 
Cohen, and Kindel 1978). 

For TNT, Figure 11 shows ion mobility spectra 
in air/nitrogen mixtures. With nitrogen carrier 
and drift gases, the major product ion is the M 
(m/z 227) ion with reduced mobility of 1.49 cm 2 
V -1 s -1 . As laboratory air is allowed to enter the 
carrier gas, the 1.49 cm 2 V -1 s _1 ion mobility peak 
decreases while the 1.54 cm 2 V -1 s" 1 ion mobility 
peak increases. The 1.49 cm 2 V -1 s“ 1 ion has been 
shown with IMS/MS to be the proton abstracted 
(M-l)~ ion. (Spangler and Lawless 1978). Figure 
12 shows Negative Chemical Ionization Mass 
Spectrometer (NCIMS) data collected against 
TNT. For these data, the molecular negative ion is 
the major ion species. This ion arises because of 
the reduced pressure and the lack of oxygen or 
NO x reactant ions in the mass spectrometer to per¬ 
form the proton abstraction reaction. The (M-l)“ 
ion was observed when the source pressure was in¬ 
creased to introduce these components. Figure 13 



DRIFT TIME (MILLISECONDS) 


Figure 8. Negative Ion Mobility Signatures for Explosive 
Vapors Using Purified Air Chemistry. Upper Signature is Re¬ 
actant Ion (Background), Other Signatures are Product Ion 
Signatures with Reactant Ion (Background) Subtraction. 


271 























CH. - ONCL 
I 

CH - 0N0 2 
I 

CH 2 - 0N0 2 




x NO“ + 
(m/z 62) 


M • NO” 


(M- xN0 3 ) 


ch 2 - 0N0 2 
I 

ch 2 -ono 2 


(N 2 )0“ 


xNO" 


+ (M-xN0 3 )* 


Figure 9. Ionization Scheme for Dynamite. 

shows Negative Atmospheric Pressure Ionization 
Mass Spectrometer (NAPIMS) data collected on 
TNT. An M~ molecular ion is observed with nitro¬ 
gen carrier gas and an (M-l)” ion is observed with 
a purified air carrier gas. TNT undergoes two 
types of reactions as displayed in Figure 14. The 
product ion depends on whether nitrogen or air is 
used as carrier gas. Electron capture reactions oc¬ 
cur in nitrogen and proton abstraction reactions 
occur in air. 

For RDX, the operating parameters used for 
IMS/MS studies are displayed in Table 2. Since 
RDX is difficult to introduce into the instrument, 
the membrane inlet was modified, as shown in 
Figure 15, to include a wire probe insertion port. 
RDX sampling was accomplished by inserting a 
wire probe dusted with RDX into the heated 
(150 °C) insertion port. 



DRIFT TIME (MILLISECONDS) 


Figure 11. Ion Mobility Signatures for 2,4,6-Trinitrotoluene 
in Air/Nitrogen Mixtures. Approximate (4% Accuracy) Mix¬ 
ture Percentages are: Spectrum A, 2% Laboratory Air; Spec¬ 
trum B, 8% Laboratory Air; Spectrum C, 10% Laboratory 
Air, Spectrum D, 15% Laboratory Air; Spectrum E, 21% 
Laboratory Air. 





I ■ . I 1 I 1 ■ 1 i . . ■ . -I . A. .. . -L I , ■ . .. . 

0 5 10 15 20 25 

DRIFT TIME (MILLISECONDS) 


30 


Figure 10. Ion Mobility Signatures for Trinitrotoluene (TNT) 
and Dynamite at Reduced Temperature (100 °C). Carrier 
Gas-Laboratory Air, Drift Gas-Prepurified Nitrogen. 


Table 2. OPERATING PARAMETERS USED FOR THE 
ANALYSIS OF RDX WITH ION MOBILITY 
SPECTROMETER/MASS SPECTROMETRY 


Ion Mobility Spectrometer 


CARRIER GAS 
DRIFT GAS 
SAMPLE GAS 
MEMBRANE 
DRIFT FIELD 
DRIFT TEMPERATURE 
INLET TEMPERATURE 


PURIFIED AIR 

PURIFIED AIR 

AMBIENT AIR 

DIMETHYLSILICONE 

194 VOLT/MC 

154°C 

170°C 


Mass Spectrometer 
PINHOLE APERTURE 25 M m 

PRESSURE 

INLET (ION FOCUS- 1.6 x 10-4 torr 

SING LENSES) 

CHAMBER (QUAD- 4x10-6 

RUPOLEMASS 

SPECTROMETER) 


Sample 

GENERATION DESORPTION IN 

HEATED INLET 


272 


















































RELATIVE INTENSITY 


OJ 

o 


cn 

O 


~>l 

O 


CO 

O 


3 OJ- 
^ O 


oi-^ 

o 


o 


CD 

O 


ro 

O 


ro 

w 

O 


-NO 


•(H 2 0)0H* 


1 -(H 2 0)0- 


=— (TNT - NO.,)' 


(TNT - NO)* 
(TNT - OH)' 


TNT' 



AIR 


NITROGEN 


Figure 12. Negative Chemical Ionization Mass Spectrometry 
of 2,4,6-Trinitrotoluene. 


Figure 16 shows the mass identified mobility 
data collected for the positive ions. The major 
ions are the m/z 75 ion with its clusters contribut¬ 
ing to the 2.26 cm 2 V -1 s _l ion mobility peak and 
the m/z 176 ion with its clusters contributing to 
the 1.64 cm 2 V -1 s“‘ ion mobility peak. Figure 17 
shows the mass identified mobility data collected 
for the negative ions. An N0 2 ion, m/z 46, is 
spread out across the spectrum, a ion clustered 
with water, m/z 258, weakly contributes to an ion 
mobility peak with reduced mobility 1.45 cm 2 V -1 
s~ 1 , and a (M-fN 0 2 )~ ion clustered with water, 
m/z 268, is a major ion species in the spectrum 
with a reduced mobility of 1.45 cm 2 V -1 s _1 . The 
ionization scheme for RDX is shown in Figures 18 
and 19. In the positive ion mode, the proton at¬ 
tacks RDX at either the nitro-nitrogen or the 
amino-nitrogen giving rise to cleavages to produce 
the m/z 75 or 176 ions respectively. In the negative 
ion mode, dissociative capture reactions lead to 
NOf which undergoes ion attachment reactions to 
produce the (M + NOD" ion. 


r*o r~o r-o 
rs> ro ro 
cn -o oo 

MASS 


Figure 13. Negative Atmospheric Pressure Ionization Mass 
Spectrometry of 2,4,6-Trinitrotoluene. Upper Signature - Air 
Carrier Gas, Lower Signature - Nitrogen Carrier Gas. 


Sample Introduction Techniques 

Table 3 lists techniques whereby sample can be 
introduced into IMS. One approach is to use an 
ambient air carrier gas with a purified air drift gas. 
The ambient air is drawn into the reactor by ap- 


CH, 


NO, 


C 

I 

HC. 


• C ^ N ° 2 


I 

.CH 


C' 

I 

NO, 



(m/z 227) 



(m/z 226) 


(Molecular Weight 227) 


Figure 14. Ionization Scheme for 2,4,6-Trinitrotoluene. 


273 
































2 26 


WIRE PROBE 
OR SYRINGE 
INSERTION 



SUCTION PUMP 

Figure 15. Modified Membrane Inlet with Probe Insertion 
Port. 


plying suction to the gas exhaust port of the IMS 
cell. Sample is introduced into the ambient air car¬ 
rier gas for analysis purposes. The early analysis 
of TNT vapor was accomplished by using this 
technique (Spangler and Lawless 1973). 

A second generation beyond the ambient air 
carrier is the membrane inlet where ambient air is 
used as sample gas and purified air is used as carri¬ 
er gas (Figure 20). The ambient air scrubs the ex¬ 
ternal surface of the membrane and the carrier gas 
scrubs the internal surface of the membrane. Sam¬ 
ple permeates through the membrane from the 
sample gas to the carrier gas. The membrane inlet 
was used for the analyses performed in connection 
with Figure 8. 

Table 3. SAMPLE INTRODUCTION TECHNIQUES 

• AMBIENT AIR CARRIER GAS 

• MEMBRANE INLET 

AMBIENT AIR SAMPLE GAS 
PURIFIED AIR CARRIER GAS 

• SAMPLE WIRE PROBE/SYRINGE 

SOLVENT EXTRACTION 
SOLVENT EVAPORATION 
ADSORPTION/DESORPTION 

• SOLIDS PROBE 

• DESORPTION OVEN 

• SURFACE SAMPLER 

THERMAL 
JET SCRUBBING 

• EXPONENTIAL DILUTION FLASK 

• STANDARDS GENERATOR 

BUBBLER 
DIFFUSION TUBE 
PERMEATION TUBE 

• GAS CHROMATOGRAPHY 



_/\_ 

/V 



m /i - 41 

/l 


(Ch^n-no 2 )h* 

m/z = 75 

A 


(n 2 )(Ch 2 -n no 2 )h* 

m/z = 103 


A 

(M-NOjl* 

m /i = 1 74 176 


/V 

(n 2 hm-no 2 )‘ 

m/z - 202-204 



(n 2 ) 2 im no 2 i* 

m/z = ^3l ^34 


Figure 16. Mass Identified Mobility Data for the Positive Ions 
of RDX. 


145 



Compatible with both the ambient air carrier 
gas and membrane inlet is the sample wire probe 


Figure 17. Mass Identified Mobility Data for the Negative Ions 
of RDX. 


274 










































































no 2 


no 2 

m/z 176 


Figurel8. Positive Ionization Scheme for RDX. 


and/or syringe. When used by itself, the sample 
wire probe collects vapor by adsorption and the 
vapor is desorbed when the wire probe is inserted 
into the heated inlet. When used with syringe, 
solvent extracts of the sample can be deposited on 
the wire probe which, after solvent evaporation, 
can be inserted into the heated inlet for sample de¬ 
sorption. The sample wire probe was used to col¬ 
lect the data of Figures 16 and 17. 

The sample wire probe and/or syringe can also 
be used to introduce sample into a purified air car¬ 
rier gas without the use of a membrane. As illus¬ 
trated in Figure 21, this is accomplished by cover¬ 
ing the inlet with a glass tube through which a hole 
is provided for insertion of the wire probe. Carrier 


ro: 1 _ 

M -?-► (H 2 0) 2 M -►(M-NO z ) + N0 ? 

m/z 258 m/z 46 

HO _ in 

-►(M + NO z ) -^-► (M + N0 2 )(H 2 0) 

m/z 268 m/z 286 


RO” ' x 

M - (M + or -► CH 2 - CH 2 + CH 2 (N - N0 2 ) 2 0~ 

m/z 150 

UNSTABLE 

I0' 5 SEC< t < I0’ 3 SEC 

Figure 19. Negative Ionization Scheme for RDX. 


gas flowing along the internal surface of the glass 
tube and into the IMS transports vapor desorbed 
from the wire probe into the IMS. The technique 
corresponds to on-stream injection in gas chroma¬ 
tography. 

A variation of the sample wire probe is the sol¬ 
ids probe. Figure 22 shows a solids probe for 
sampling soil. It consists of an 0.25 inch diameter 
stainless steel tube specially configured to accept 
the soil particles. Sample air for the IMS flows 
through the stainless steel tube, across the soil par¬ 
ticles, and into the IMS. The experiment consists 
of exposing the soil particles to head space vapors 
of TNT, placing the soil particles in the solids 
probe, and inserting the solids probe into the 
heated inlet of the instrument. Desorption of 
vapor from the soil particles yields a strong re¬ 
sponse from the IMS instrument. 

The desorption oven technique consists of flow¬ 
ing carrier gas through a sealed oven before enter¬ 
ing the IMS. Materials to be sampled are placed in 
the oven and heated. Vapors released from the 
sample materials are then carried into the IMS by 
the carrier gas. Carr and Needham used this tech¬ 
nique to study impurities on silicon discs (Carr 
and Needham 1979). The technique is also used at 
Bendix to screen materials for IMS construction. 

The exponential dilution flask and standards 
generator techniques are calibration techniques. 
The exponential dilution flask was used to estab¬ 
lish the basic limit of detection of 0.1 ppt for IMS 


275 




















PUMP IN CONNECTOR 

8200I-54A 

Figure 20. Membrane Inlet System for Ion Mobility Spectrometry. 

circulates the gases through a molecular sieve trap 
to purify them before entering the IMS. The mem¬ 
brane isolates the ambient air from the internal 
workings of the IMS cell. Thus the water, am¬ 
monia, NO x and halogenated vapor components 
of ambient air are excluded from the reactor of 
IMS. These problem vapors influence the 
ion/molecule reactions needed to ionize sample. 
IMS/MS data on the nature of reactant ions in 
IMS using a membrane inlet is submitted for pub¬ 
lication (Spangler and Carrico 1983). 

The top panel of the compact IMS of Figure 23 
is shown in Figure 25. The sample port going to 
the membrane enters through this panel. The LED 
readout is operator accessed to determine the state 
of the instrument and to specify the compound 
giving rise to an alarm. Compounds are specified 
by the microprocessor from features of the ion 
mobility spectrum. An alarm horn provides an 
audible alarm in the presence of targeted vapor. 
Outputs are available for oscillocope or signal 
averager display. An RS232 interface is available 
to transmit IMS signatures over telephone lines 
from the system to a host computer. 

Surface sampling can be accomplished by at¬ 
taching a surface sampler to the inlet of the system 
of Figure 23 as illustrated in Figure 26. The func¬ 
tion of the surface sampler is to heat the sample on 


to TNT vapor (Spangler and Lawless 1978). Diffu¬ 
sion tube generators have been used to establish 
the limit of detection of approximately 1 ppb for 
IMS (with a membrane inlet) to organophosphor¬ 
ous vapors (Carrico, Campbell, and Spangler 
1983). 

Ion Mobility Detector System 

A compact IMS system with a membrane inlet is 
displayed in Figure 23. The system is 0.6 cu. ft. in 
volume, weighs less than 30 pounds and is micro¬ 
processor controlled. The system requires a 28 volt 
power supply for operation and draws under 50 
watts. It can be carried very easily by one man 
with the handle/roll-bar. 

The pneumatic and electronic layout for the sys¬ 
tem is illustrated in Figure 24. A closed loop is 
provided for the carrier and drift gases. A pump 


RADIOACTIVE 
SOURCE 

ROOM f ~ -. -...Aj yvr 

A,R 

- 

CARRIER 
GAS 

Figure 21. Wire Probe Insertion Inlet with Postulated Flows. 


EXIT 



EXIT 


276 



























































SOLIDS PROBE 


PLASMA CHROMATOGRAPH 


Figure 22. Solids Probe for the Analysis of Explosive Vapors Adsorbed on Soil Particles. 



Figure 23. A Compact Ion Mobility Detector System for 
Monitoring Ambient Air. 


277 








SYSTEMS DIAGRAM 


28 VDC 
IN 

O- 


LOW VOLTAGE 
POWER SUPPLY 


HIGH VOLTAGE 
POWER SUPPLY 


CELL CONTROL ELECTRONICS 

VOLTAGE 

ISOLATION 

AND 

BIASING 

PULSE 

GENERATOR 


CELL HEATER 
SUPPLY ANO 

CONTROL CIRCUITS 


DIME THYLSILIC ONE 
MEMBRANE\ 


SAMPLE IN 



MICROPROCESSOR 


DATA 

• ACQUISITION 

• Signal averaging 

• digital FILTERING 

• peak NORMALIZATION 

• FEATURE EXTRACTION 

• ALARM 

• SIGNATURE STORAGE 
SYSTEM CONTROLS 

•CELL POLARITY 

• calibration 

• SHUTTER GRID CONTROL 

• OPERATOR INTERFACE 

• REMOTE TRANSMISSION 

• SYSTEM CHECKS 


-OMNI SWITCH 


► lED Display 


► SCOPE DISPLAt 


► RS232 link 


Figure 24. The Pneumatic and Electronic Layout for the System of Figure 23. 



Figure 25. Top Panel for the System of Figure 23. 


the surface and transport the released vapors to 
the detector which functions as a normal alarm. A 
closer view of the surface sampler is presented in 
Figure 27 and an internal schematic is shown in 


Figure 28. In the sampler is a tungsten halogen 
lamp to heat the surface and air jets to cause tur¬ 
bulence in the sampler cone. The sample released 
from the surface swirls up into the transport lines 


278 















































































Figure 26. Surface Sampler Attached to the Inlet of the System of Figure 23. 



Figure 27. Close-Up View of the Surface Sampler. 


which carry the sample to the detector. 

Figure 29 illustrates the theoretical considera¬ 
tions underlying the design of the surface sampler. 
A high flow of gas is maintained across the surface 
to reduce stagnant boundary layers which impede 
the flow of released vapors. As given by the diffu¬ 
sion equation, the flux, J v , of vapor across the 
boundary layer, 6, is proportional to the square 
root of gas velocity. Because the concentration of 
vapor delivered to the detector is the flux divided 
by the gas velocity, the sample concentration 


sensed by the detector is inversely proportional to 
the square root of the gas velocity. To both main¬ 
tain high velocities required to reduce boundary 
layer effects while at the same time to maintain 
low velocities required to minimize sample dilu¬ 
tion effects, localized air jets are used to scrub the 
surface. 

The concentration term (ne-n v ) of J v is the 
gradient which drives the vapor release. This term 
is temperature sensitive since n e corresponds to the 
equilibrium vapor pressure of sample at surface 


279 





LAMP "ON" 
WARNING LIGHT 



HANDLE 



HEATED SAMPLE AND 
JET AIR LINES 


Figure 28. Internal Drawing of the Surface Sampler. 


temperature. The tungsten-halogen lamp in¬ 
creases the surface, and hence sample tempera¬ 
ture, to increase n e . Such an increase leads to 
greater sampling efficiency for the surface 
sampler. 

Finally, the flux J v is inversely proportional to 
the dimension L of the channel in which the gas 
flows. A collapsed geometry for the sampler cone, 



Surface 


LANGMUIR DIFFUSION EQUATION 

J v=4[n e -n v ] 

VISCOUS BOUNDARY LAYER 

s = where R = e -~ : 

fW * 

THEREFORE 

n e -n v 



where L is small, is preferred over open geometry. 
This is illustrated in Figure 30 where configuration 
A is preferred over configuration B. In practice, 
however, the greater effectiveness obtained from 
jet scrubbing (configuration C) and heating with 


Q Q 




6 6 



Figure 29. Theoretical Considerations for the Operation of the 
Surface Sampler. 


280 


Figure 30. Surface Sampler Cone Geometry. 






















































































































SIGNAL PROCESSOR 



Figure 31. Surface Sampler Closely Coupled to a Hand-Held Ion Mobility Spectrometer. 


the tungsten-halogen lamp (configuration D) ex¬ 
ceeds the losses associated with the open geometry 
needed to implement these techniques. Between jet 
scrubbing and heating, heating was found more 
effective depending on surface composition. 

Finally, Figure 31 shows a surface sampler 
closely coupled to an IMS in an hand held con¬ 
figuration. The direct coupling between the sur¬ 
face sampler and IMS cuts down transmission 
losses for the vapors through connecting tubes. 

Acknowledgements 

The authors wish to acknowledge G. Sima, K. 
Vora, J. White and J. Roehl as the principal en¬ 
gineers for the design of the compact IMS system. 
The authors wish to acknowledge G. Lozos for the 
design and testing of the surface sampler. The en¬ 
couragement and interest of D. Campbell during 
the development efforts is acknowledged. 

REFERENCES 

Asse/in, M. (1978). Detection of Dynamite with a 
Plasma Chromatograph. Proceeding’s New 
Concepts Symposium and Workshop on Detec¬ 
tion and Identification of Explosives, Reston, 
VA. 


Carr, T. W. and Needham, C. D. (1979). Analysis 
of Organic Surface Contamination by Plasma 
Chromatography/Mass Spectroscopy. Surface 
Contamination: Genesis, Detection, and Con¬ 
trol, Plenum, NY, pp 819-829. 

Carrico, J. P., Campbell, D. N., and Spangler, 
G. E. (1983). A Compact Ion Mobility Spec¬ 
trometer System. Paper 91, 1983 Pittsburgh 
Conference on Analytical Chemistry and Ap¬ 
plied Spectrometry, Atlantic City, NJ. 

Carrico, J. P., Dick, K. A., Spangler, G. E., 
Lozos, G. P., White, R. J., Bottorf, R. J., 
Roehl, J. E., and Vora, K. N. (1982). Feasibili¬ 
ty Studies for the Advanced Chemical Agent 
Detector Alarm. Final Technical Report, Con¬ 
tract D A AK11-80-C-0024, ARCSL-CR, 

USAR-RADCOM, Chemical Systems Labora¬ 
tory, Aberdeen Proving Ground, MD 21010. 

Karasek, F. W. (1974). Plasma Chromatography. 
Anal. Chem. 4<5(8):710A-720A. 

Mason, E. A., O'Hara, H., and Smith, F. J. 
(1972). Mobilities of Polyatomic Ions in Gases; 
Core Model. J. Phys. B: Atom. Molecul. Phys. 
5:169-176. 

Mason, E. A., and Schamp, H. W. (1958). Mo¬ 
bility of Gaseous Ions in Weak Electric Fields. 
Ann. Phys. 4:233-210. 


281 































Spangler, G. E. (1978). Principles Underlying the 
Performance of Ionization Detectors for Explo¬ 
sive Vapor Detection. Proceeding’s New Con¬ 
cepts Symposium and Workshop on Detection 
and Identification of Explosives, Reston, VA. 

Spangler, G. E. and Carrico, J. P. (1983). Mem¬ 
brane Inlet for Ion Mobility Spectrometry 
(Plasma Chromatography). 52:267-287. Int. J. 
Mass Spectrum, and Ion Phys. 

Spangler, G. E., Carrico, J. P. and Campbell, 
D. N. (1983). Recent Advances in Ion Mobility 
Spectrometry for Explosive Vapor Detection. 
Proceeding’s Explosives Detection for Security 
Applications, ASTM, Philadelphia, PA. 

Spangler, G. E. and Lawless, P. A. (1978). Ioni¬ 


zation of Nitrotoluene Compounds in Negative 
Ion Plasma Chromatography. Anal. Chem. 
50(7):884-892. 

Spangler, G. E., Suh, S. W. and Carrico, J. P. 
(1980). Single Stage Membrane Separator for 
Ion Mobility Spectrometry (Plasma Chroma¬ 
tography). Paper 549, 1980 Pittsburgh Confer¬ 
ence on Analytical Chemistry and Applied 
Spectrometry, Atlantic City, NJ. 

Wernland, R. F., Cohen, M. J. and Kindel, R. C. 
(1978). The Ion Mobility Spectrometer as an 
Explosive or Taggant Vapor Detector. Proceed¬ 
ing’s New Concepts Symposium and Workshop 
on Detection and Identification of Explosives, 
Reston, VA. 


282 


HIGH PERFORMANCE LIQUID 
CHROMATOGRAPHY METHODS 





































































































THE ANALYSIS OF ETHYLENEGLYCOLMONONITRATE AND 
MONOMETHYLAMINE NITRATE FROM COMMERCIAL BLASTING 

AGENTS IN POST BLAST SAMPLES 


R. J. Prime, Ph.D. and J. Krebs 
Centre of Forensic Sciences 
Toronto, Canada 

ABSTRACT. The analysis for ethyleneglycolmononitrate and monomethylam- 
ine nitrate in commercial blasting agents and post blast samples has been done. The 
commercial blasting agents, POWERMEX (C.I.L.) and TOVEX (DuPont) have 
been encountered in an number of seized, disrupted or hoax explosive devices and 
have been suspected in a number of bombing incidents. Work has been done to de¬ 
velop a procedure to detect the sensitizers ethylenglycolmononitrate (EGMN) from 
Powermex and monomethylamine nitrate (MMAN) from Tovex using high per¬ 
formance liquid chromatography. Analysis of samples of debris recovered from 
test blasts has been successful after using an appropriate pre-concentration tech¬ 


nique. 

INTRODUCTION 

Powermex® and Tovex® are commercial blast¬ 
ing agents available in Canada for about 10 years. 
Although marketed as replacements for dynamite 
they have not succeeded in displacing its popular¬ 
ity particularly in the criminal community. Never¬ 
theless, they have been found amongst explosives 
confiscated from motorcycle gangs and have been 
suspected in a number of bombings in labour re¬ 
lated incidents in areas where there is ready access 
to these particular products. Thus a method of 
analysis is needed. 

Powermex® and Tovex® are sensitized with 
ethyleneglycolmononitrate (EGMN) and mono¬ 
methylamine nitrate (MMAN) respectively. The 
purpose of this project was to develop a technique 
for the qualitative identification of small amounts 
of EGMN and MMAN and to determine whether 
detectable amounts of these sensitizers can be 
found in post blast debris. Further, it is desirable 
that the method be compatible with that devised 
for the analysis of dynamite residues previously 
reported by Prime and Krebs (1980). 

Because it is chemically similar to ethylenegly- 
coldinitrate (EGDN) and nitroglycerine, EGMN 
can be identified following a procedure analogous 
to that described for dynamite. On the other hand, 
MMAN is a chemically unrelated compound. 

The identification of MMAN in large samples 
can be done by X-ray diffraction and infra-red 


spectrophotometry. However, for smaller 
amounts dispersed in explosion debris, the recov¬ 
ery and identification of MMAN is more difficult. 
Parker (1975) has described some properties of 
MMAN and spot tests for identification; also the 
literature [Kuwata et al. (1980) and Blau and King 
(1978)] suggests a variety of methods for the anal¬ 
ysis of amines by both gas chromatography and 
derivative high performance liquid chromatog¬ 
raphy (HPLC). A procedure involving extraction 
and derivatization of the monomethylamine for 
subsequent identification by HPLC was selected. 

EXPERIMENTAL 
Equipment and Materials 

A Waters ALC 202 liquid chromatographic sys¬ 
tem with 6000A pumps, a model 660 solvent pro¬ 
grammer, and a U6K septumless injector (Waters 
Associates, Milford, Mass.) was used. A variable 
wavelength Spectromonitor II model 1202 (LDC, 
Riviera Beach, Florida) UV-visible detector was 
used. 

Solvents were HPLC-grade supplied by Cale¬ 
don (Georgetown, Ont.), filtered and degassed by 
suction through 0.5 p Teflon filters (Millipore, 
Bedford, Mass.). Water used for chromatography 
was glass distilled and organic contamination was 
removed with a Norganic cartridge (Millipore). 

Columns were /j-Bondapak-CN and p-Bonda- 


285 


pak-Cis (Waters Assoc.) supplied prepacked in 3.9 
mm x 30 cm stainless steel. 

EGMN, MMAN were prepared as standards in 
this laboratory. The explosives were 1" x 12" 
sticks of CIL Powermex® 300 and Dupont 
Tovex® 5000 SB initiated with No. 8 electric blast¬ 
ing caps. 

Dansyl chloride (Fisher Scientific, Toronto) was 
used as supplied. 

Tests 

Two separate blast sites were used to provide 
different types of debris. 

(a) Single sticks of blasting agent were deto¬ 
nated on clean sand. Samples were collected from 
the base and edges of the crater to a depth of 2-3 
cm and stored in 1 1 Mason jars. 

(b) To simulate a common explosion site, a 
four foot square wooden frame was constructed 
of 2" x 4" lumber with studs at 16" centre. The 
spaces were filled with R-12 fiberglass insulation 
and the unit covered with drywall. The single 
sticks of blasting agent were taped to the centre of 
the drywall, draped with curtain and detonated. 
Samples of fiberglass and drapery were collected 
from the edges of the seat. 

H B 

201 
50 1 


Procedure 

/. Ethyleneglycolmononitrate 
Samples to be tested were purged for 1 hr. with 
N 2 at room temperature and at 65 °C and the efflu¬ 
ent collected on charcoal using a 700 ml glass ap¬ 
paratus as previously described for the recovery of 
EGDN and nitroglycerine by Prime and Krebs 
(1980). Each trap was washed with 1 ml of 
2-propanol which was then filtered through a 0.5 
^ Teflon filter. A 5 \jI portion of this was run di¬ 
rectly on HPLC. The remainder was concen¬ 
trated, when necessary, by evaporation under an 
air stream being careful not to take to dryness. 
Monomethylamine nitrate 
A 500 to 700 cc portion of the material from the 
seat of the explosion was washed with a minimum 
of distilled water (usually 50 to 100 ml) and fil¬ 
tered. The solution was made acidic with hydro¬ 
chloric acid, then taken to dryness on a steam 
bath. The residue was re-dissolved in 1 ml water 
and added to 3 ml of DnsCl in acetone. Na 2 C0 3 
was added to make the solution basic (usually 10 
mg) and the mixture shaken vigorously; then, 
stored at 45 °C for 30 min. in darkness. The Dns 
derivative was recovered by extraction with 5 ml 


IONDAPAK C 18 
O nm 

SO acetonitrile'water 


pBONDAPAK CN 
254 nm 

70«30 hexane*chloroform 


H BONDAPAK CN 
214 nm 

90<10 hexane*isopropanol 


egdn 


egmn 

egdn 


jU 


ng 





egmn 



O 5 10 15 

Figure 1. Separation of EGMN, EGDN and nitroglycerine using various chromatographic conditions. 


286 



































of n-heptane which was evaporated on a steam 
bath. The residue was taken into 1 ml acetonitrile. 
A 5 [xi portion of this was injected into the liquid 
chromatograph. 

RESULTS AND DISCUSSION 

Figure 1 shows the separation of EGMN, 
EGDN and nitroglycerine using various chroma- 


fj BONDAPAK CN 
224 nm 

10% 2-propanol in hexane 


flowrate : 1 ml /min 



Ethyleneglycolmononitrate recovered from 
fibreglass debris after a POWERMEX 
test blast 

Figure 2. EGMN recovered from fiberglass debris after a 
Powermex® test blast. 


tographic conditions. The sensitivity for these 
compounds is increased at lower wavelengths, 
therefore, the choice of wavelength is governed by 
the transparency of the mobile phase. 

EGMN was recovered from samples in both 
tests and Figure 2 shows the recovery of EGMN 
from fiberglass. Recovery of EGMN was en¬ 
hanced by at least a factor of 4 by purging at 
65 °C. In the general approach to recovery, a room 
temperature purge of explosion debris is still a 
worthwhile step, particularly, for samples that are 
likely to contribute interfering contamination on 
heating. 

Verification of EGMN can be made by altering 
the chromatographic conditions as seen in Figure 
1 or by gas chromatography, Yip (1982). 

Figure 3 shows the separation of the methyl- 
amine dansyl derivative from the excess reagent. A 

2 

I 

p BONDAPAK C )8 
254 nm 

49% - 70% CH 3 CN in water 
Curve program 9 in 7 minutes 



Dansyl derivatives of extract of fibreglass debris 
from TOVEX blast: 1 . ammonia 2. methylamine 
3. reagent 

Figure 3. Dansyl derivatives of extracts of fiberglass debris 
from a Tovex® test blast: 1. ammonia 2. methylamine 3. re¬ 
agent. 


287 






















1 

[i BO N DA PA K C 18 
254 nm 

49% - 70% CH 3 CN in water 
Curve program 9 in 7 minutes 

flowrate : 1 ml/min 



0 min 5 10 IS 

Dansyl derivatives of : 

1. ammonia 2. methylamine 3. ethylamine 4. dimethylamine 

Figure 4. Dansyl derivatives of: 1. ammonia 2. methylamine 
3. ethylamine 4. dimethylamine. 

peak often appears for the ammonia derivative 
due to the ammonium nitrate in Tovex® but pre¬ 
sents no problems. 

Unlike EGMN, EGDN and nitroglycerine, pri¬ 
mary amines are not specific to explosive sub¬ 
stances. Thus it is particularly important that 
comparison samples unaffected by the blast be 
examined before conclusions are reached. Other 
low molecular weight aliphatic amines were de- 


rivatized and could be separated from the methy¬ 
lamine derivative by HPLC as seen in Figure4. 

The general approach to explosive debris allows 
for the recovery of EGMN, EGDN and nitrogly¬ 
cerine by the purge and trap procedure followed 
by extraction with water for MMAN. Since nitrate 
crystals, and other physical evidence are often use¬ 
ful to the investigation, a microscopic examina¬ 
tion is necessary. This can be accommodated after 
the purge and before the extraction step since 
MMAN is not volatile. 

Of further interest from the test blasts was the 
fact that without a booster charge Tovex® very 
often did not detonate completely and pieces were 
sometimes visible in the debris or as smears on the 
drywall surface. Furthermore, both Tovex® and 
Powermex® left numerous fragments of plastic 
wrapper many of which had useful identification 
value. 

CONCLUSION 

EGMN and MMAN can be recovered from ex¬ 
plosion debris by a procedure that is compatible 
with that used for the recovery of the explosive 
oils of dynamite which are more commonly en¬ 
countered. 

REFERENCES 

1. Blau, K., King, G. S., Handbook of Deriva¬ 
tives for Chromatography, Heyden London 
1978, p 349 ff. 

2. Kuwata, K., Yamazaki, Y., Vebori, A/., Deter¬ 
mination of traces of low aliphatic amines by 
gas chromatography, Anal. Chem. 52 (1980), 
1980. 

3. Parker, R. G., Analysis of explosives and ex¬ 
plosive residues. Part 3. Monomethylamine ni¬ 
trate, J. of Forens. Sci. 20 (1975) 257. 

4. Prime, R. J., Krebs, J., The recovery and iden¬ 
tification of ethyleneglycoldinitrate and nitro¬ 
glycerine in explosion debris using preconcen¬ 
tration and high performance liquid chromatog¬ 
raphy, Can. Soc. Forens. Sci. J. 13 (1980) 27. 

5. Yip, I. H. L., A sensitive gas chromatographic 
method for analysis of explosive vapours, Can 
Soc. Forens. Sci. J. 15 (1982) 87. 


288 



















ANALYSIS OF EXPLOSIVES BY HPLC-FTIR 


Randall H. Riddell, B.S. 
and 

Terry Mills, III. M.S. 
Georgia State Crime Laboratory 
Atlanta, Georgia 


ABSTRACT. High pressure liquid chromatography (HPLC) is gradually sup¬ 
planting thin layer chromatography (TLC) as a tool in the identification of explo¬ 
sive residues. Debris from explosion scenes is often extracted using bulk solvents or 
by headspace concentration and analyzed by HPLC. Identifications are based on 
comparison of retention time data with known standards. It would be desirable, 
however, to develop a more specific method for identification of these eluants us¬ 
ing Fourier Transform Infrared Spectroscopy (FTIR). The tremendous separatory 
power of HPLC allows the analyst to “prep” each component of the explosive 
residue in suitable purity and quantities to generate useful infrared spectra. Nor¬ 
mal phase HPLC with 3 micron silica columns is particularly useful because elu¬ 
ants are then composed of organic solvents which are readily evaporated to yield a 
film on KBr plates or a pressed KBr pellet of the sample. Since FTIR has proven to 
be considerably more sensitive than dispersive IR, the FTIR systems can be used as 
a real-time chromatographic detector. Using ultra-micro HPLC flowcells (0.2 pi 
volume) as detector cells, the FTIR becomes an on-the-fly detector. Special soft¬ 
ware, such as the Nicolet chemigram programs, and liquid nitrogen cooled 
Mercury Cadmium Telluride detectors serve to provide a very selective detector 
sensitive only to changes in absorptions in a narrow infrared wavelength region. 
Alternatively, the full spectra can be taken of the eluant on-the-fly. Subtraction 
routines then can be used on this data to remove the contribution the eluant sol¬ 
vents to the eluate spectrum. The resultant spectrum then can be confirmed by 
comparison with reference spectra via a computer library search of various stand¬ 
ard explosive infrared spectra. 


INTRODUCTION 

The criminal use of explosives appears to be on 
the rise in this state. Recently there have been two 
bomb-related deaths, one exploding device in an 
automobile causing permanent injury, and a num¬ 
ber of “damage to property” cases. This trend has 
prompted a search for improvements in the anal¬ 
ysis of explosive residues. 

One such improvement is the use of high pres¬ 
sure liquid chromatography (HPLC) to aid in the 
screening and identification of commonly en¬ 
countered explosives. Both normal and reversed 
phase separations with UV detection for the nitro- 
aromatics, nitrate esters and nitramines have pre¬ 
viously been reported. 1 4 In this laboratory HPLC 
has been augmenting analysis schemes using TLC, 
IR, XRD, chemical spot tests and microchemical 


tests similar to those already demonstrated. 5 ' 10 De¬ 
bris from explosion scenes are usually extracted 
using bulk solvents or by headspace concentra¬ 
tion" and analyzed by HPLC using retention time 
data for identification. 

UV detection at 254 nm is a relatively non-selec- 
tive technique because many other compounds, 
such as asphaltics, plasticizers and other co-ex- 
tractables, absorb at that wavelength to give a de¬ 
tector response. A recent improvement in HPLC 
selectivity has been proposed by interfacing the 
chromatograph with a Fourier transform infrared 
spectrometer (FTIR). 12,13 Wavelengths characteris¬ 
tic of functional group absorptions in certain ex¬ 
plosives would give confirmation of the un¬ 
knowns’ identity when combined with the reten¬ 
tion time as the component elutes from the ana- 


289 


lytical column. Furthermore, it would be even 
more desirable to generate a complete IR spectrum 
of the component. By subtracting absorptions due 
to solvent, it is possible to show all the absorption 
bands at their characteristic frequencies in the fin¬ 
gerprint region. 

The FTIR has several advantages over conven¬ 
tional dispersive instruments: fast, sensitive MCT 
detectors; 14 high scan velocities and data collec¬ 
tion rates; small beam size; and photometric scale 
accuracy. The detection of HPLC eluates can be 
accomplished by two methods. The first method is 
an off-line approach. This method involves col¬ 
lecting the fraction as it elutes, using the UV detec¬ 
tor response to indicate when to collect the sam¬ 
ple, evaporating the solvent and then making a 
KBr disc for a complete IR scan. The second 
method is direct detection via a flow cell in an 
on-line manner, thus avoiding possibilities of con¬ 
tamination, moisture uptake or other changes 
which might occur on collection and storage. 

Two major problems concerning on-line 
HPLC-FTIR are regions of the spectrum blanked 
by solvent absorptions (opacity) and the phenome¬ 
non of solute-solvent interactions shifting solute 
absorption bands. These problems investigated in 
this study have been dealt with previously. 15 

Another potential problem with HPLC-FTIR is 
the development of a system that will separate the 
mixtures chromatographically without interfering 
with the IR detection. The solvent programming 
usually employed in HPLC separations results in a 
constantly changing background spectrum that is 
not easily subtracted. However, isocratic flow 
programming is permissible (within the pressure 
limits of the system) as the IR detector is insensi¬ 
tive to flow rate. 

EXPERIMENTAL 

Materials 

The explosive mixture used in this study con¬ 
tained 1 mg each of nitroglycerin (NG), pentery- 
thritol tetranitrate (PETN), trinitrotoluene (TNT) 
and cyclotrimethylene trinitramine (RDX) in 1.0 
mL chloroform (Fisher Scientific, HPLC grade). 
These high explosives were obtained by solvent ex¬ 
traction and recrystallization of military explo¬ 
sives using detonating cord (PETN), military 
TNT, and C-4 plastic explosive (RDX). The nitro¬ 
glycerin was obtained from 0.6 mg Nitrostat tab¬ 
lets (Parke-Davis). 


Chromatograph 

A Varian model 5000 chromatograph with a 
Valeo loop-valve injector and a 3 micron 
Adsorbosphere column (Applied Science Labs, 10 
cm x 4.6 mm) fitted with a direct-connect guard 
column (Applied Science Labs) and packed with 
20 micron porous silica were used for all separa¬ 
tions. All connecting tubing was 0.25 mm i.d. 

The flow rate was 0.5 mL/min with a column 
“dead volume’’ of 0.4 milliliters. An isocratic 
50/50 mixture of cyclohexane/methylene chloride 
(Fisher Scientific, HPLC grade) solvent system 
was used. 

Two flow cells were utilized. The larger cell’s 
dimensions were 0.2 mm pathlength and 3 mm i.d. 
(Nicolet Instrument Corporation). The smaller 
flow cell was an ultramicro cavity flow cell with a 
0.05 mm pathlength and 0.2 microliter volume 
(Barnes Analytical). Both cells were constructed 
with KBr windows and low dead volume fittings. 

Spectrometer 

A Nicolet 7199 FTIR with a normal KBr-Ge 
beam splitter was used for all infrared measure¬ 
ments. This spectrometer includes a laser-refer¬ 
enced Michelson interferometer with an absolute 
wavenumber accuracy specified better than *0.01 
cm '. The detector was a liquid nitrogen cooled 
mercury-cadmium telluride (MCT-A) detector, 
7000 to 700 cm' 1. The operating software used 
was supplied by the manufacturer. All data were 
acquired with a mirror velocity of 0.880 cm/sec 
and 4096 data points per scan. These conditions 
resulted in a constant resolution of 4 cm’ 1 . 

EXPERIMENTAL RESULTS 

A preliminary evaluation of the chromato¬ 
graphic system ( i.e . normal or reversed phase) 
along with the optimized operating parameters are 
shown: 


CHROMATOGRAPHIC PARAMETERS 

HPLC: VARIAN model 5000 

COLUMN: 3 u ADSORBOSPHERE 10 cm x 4.6 mm 
(APPLIED SCIENCE) 

DETECTOR: 254 nm UV 
FLOW RATE: 0.5 ml/min 

SOLVENT SYSTEM: 50:50 METHYLENE CHLO¬ 
RIDE/CYCLOHEXANE 

STANDARDS: TNT,NG, PETN,RDX (1 mg/ml) 
INJECTION VOL: 30wl 


290 


NORMAL PHASE 

Solvents transparent in 1R region of interest 

Solvents amenable to other methods of analysis (eg) mass spec. 

Column life generally superior 

REVERSED PHASE 

Generally superior separation 
Solvents better for explosives 

Retention times were 3.5 min (TNT), 6.9 min 
(NG), 7.0 min (PETN) and 83.5 min (RDX). The 
solvent composition was changed to 90% methyl¬ 
ene chloride for RDX to speed analysis time. 
While this separation leaves room for improve¬ 
ment, it is preferable to a reversed-phase system 
( e.g . water and acetonitrile) due to difficulties in 
solvent subtraction routines in the infrared 
analysis. 

The pure explosives were prepared for spectral 
analysis with KBr discs. Using a 30 jd injection, all 


compounds were chromatographed individually. 
The eluted species were collected, evaporated to 
dryness and pressed into KBr discs for spectral 
analysis and comparison. 

On-the-fly real time measurements were in¬ 
vestigated using Nicolet’s chemigram software 
program. This program enables the FTIR to 
simultaneously monitor in real time several 
absorption bands. By setting the wavenumber 
range for each of four chromatographic windows, 
corresponding to each explosive, the FTIR was 
able to monitor and store any integrated absor¬ 
bance that exceeded a preset threshold. In this 
manner, the chemigram produced a chromato¬ 
gram similar to the UV detector output. Further, 
the complete IR spectra of the component was col¬ 
lected and stored in absorbance files for future 
use. A representative chemigram plot of a nitro¬ 
glycerin sample (30 /jg) is shown along with its re¬ 
sultant on-the-fly IR spectrum. 


GA STATE CRIME LAB 



291 







































GA STATE CRIME LAB 



Figure 2 


292 


























TRANSMITTANCE 


GA STATE CRIME LAB 



Figure 3 


293 























































GA STATE CRIME LAB 



Figure 4 


294 





























































GA STATE CRIME LAB 



Figure 5 


295 



















GA STATE CRIME LAB 



Figure 6 


296 












GA STATE CRIME LAB 



Figure 7 


297 






























GA STATE CRIME LAB 



Figure 8 


298 

























299 



















































































































































































































































Figure 10 


Each on-the-fly spectrum represents a collec¬ 
tion of 16 scans using rapid scanning techniques (8 
seconds elapsed time). This high speed scan rate 
permits the acquisition of a relatively large num¬ 
ber of averaged signals in a time interval compat¬ 
ible with the residence time of the eluant in the 
flow cell. 

The interval of time required for the eluant to 
travel from the UV detector, via the connecting 
tubing, to the flow cell in the 1R was eleven sec¬ 
onds. This information enabled the development 
of a suitable stop-flow technique. At precisely 
eleven seconds after the maximum UV absorbance 
was observed on the HPLC recorder, the LC 
pump was shut off and the purge valve opened. 
This prevented back pressure from slowly displac¬ 
ing the analyte from the flow cell. At this point 


1000 scans were collected, ratioed to an appro¬ 
priate stored solvent background, and displayed. 

Multiple runs showed this technique to be re¬ 
producible. The blank region (flat line) in each of 
the spectra between 700-400 cm" 1 corresponds to 
the cut-off region of the MCT detector. The blank 
region in the RDX spectra (ca. 2800 cm" 1 ) repre¬ 
sents solvent opacity. Incomplete subtraction of 
solvent is also denoted by the small triangles in the 
stop-flow and on-the-fly spectra. Some negative 
deviations are also observed in the nitroglycerin 
spectrum due to solvent absorptions. 

It was determined that the small flow cell (0.2 /il 
volume) produced significantly better results than 
the larger volume flow cell. A background spec¬ 
trum of the solvent in the ultramicro flow cell was 
stored for ratioing and subtraction routines. 


300 




























































TRANSMITTANCE 


GA STATE CRIME LAB 



Figure 11 


301 












TRRNSMITTANCE 


GA STATE CRIME LAB 



Figure 12 


302 



















GR STRTE CRIME LRB 



Figure 13 


303 













TRANSMITTANCE 


GR 5TRTE CRIME LRB 



Figure 14 


304 

























V. TRANSMITTANCE 


GA STATE CRIME LAB 



Figure 15 


305 




















































TRANSMITTANCE 


O 

o 


GA STATE CRIME LAB 



Figure 16 


DISCUSSION 

The isocratic HPLC solvent system used proved 
to be well suited to subtraction routines. Only the 
N-O symmetric stretching of the nitrate esters at 
1280 * 10 cm' 1 was close to the solvent absorption 
at 1260 cm' 1 . In general the major functional 
group absorbances for the explosives in this study 
were not affected significantly by the solvent. 

Solute-solvent interactions were observed by 
comparing the IR spectra of the pure compound 
with those in dilute solution. Band shifts and band 
broadening appeared to be minor, approximately 
5 cm -1 . This band shifting occurred with the simi¬ 
lar nitrate esters. Observing the change from pure 
compound to the compound in solution, a doublet 
is clearly seen at ca. 1290 cm 1 for NG. The oppo¬ 
site effect occurs for PETN, an original triplet 
changing to a single band in the same wavenumber 
range. These effects were reproduced in consecu¬ 
tive analyses in this concentration range. 

The solvent subtraction routines were per¬ 
formed by ratioing the solvent plus sample spec¬ 


trum to solvent background spectrum. Perfect ra¬ 
tioing is only possible if no interactions occur be¬ 
tween the two. This method is theoretically correct 
for dilute solutions. At high solute concentrations 
a slight negative spectrum was observed represent¬ 
ing displacement of solvent by the sample. The at¬ 
tempt to minimize this displacement by increasing 
the solvent size proved to make the subtraction 
less effective. 

Detection limits were not an objective of this 
study and would depend on the molar absorptivity 
of the analyte along with the chromatographic 
peak volume. The working amount of explosive 
detected was 30 ^g which should be the approxi¬ 
mate sample weight in the flow cell. With more di¬ 
lute solutions an order of magnitude in sensitivity 
should be attainable by increasing the number of 
scans and optimizing the sharpness of the chroma¬ 
tographic elution band. The faster, more sensitive 
MCT detector used in this study is a necessity 
since the conventional TGS room-temperature de¬ 
tector showed insufficient sensitivity in this in¬ 
vestigation. 


306 























CONCLUSIONS 

This HPLC-FTIR system permits on-the-fly 
real time measurements in flow cells thin enough 
to overcome solvent opacity in the analysis of rela¬ 
tively concentrated solutions. For more dilute 
solutions, such as traces of explosives, the use of 
the stop-flow method to obtain a complete IR 
spectrum is superior. This technique of using 
and/or identifying characteristic molecular fre¬ 
quencies at a particular chromatographic reten¬ 
tion time enables the forensic chemist to make a 
complete identification of the explosive. 

Further developments in this laboratory with 
this system hopefully will include optimizing de¬ 
tection to sub-microgram levels. Improvements 
are needed in the separation and identification of 
NG and PETN. Indexing the UV absorbance to 
the IR absorbance at a characteristic wavelength 
should increase the specificity of this method. 


REFERENCES 

(1) Dalton, R. W., Chandler, C. D., and Bol- 
leter, W. T., “Quantitative liquid chromato¬ 
graphic analysis of propellants containing nitro¬ 
glycerin”, J. Chromatogr. Sci., Vol. 13, 1975, 
p. 40. 

(2) Doali, J. O. and Juhasz, A. A., “Application 
of high speed liquid chromatography to the 
qualitative analysis of compounds of propellant 
and explosives interest”, J. Chromatogr. Sci., 
Vol. 12, 1974, p. 51. 

(3) Farey, M. G. and Wilson, S. E., “Quantita¬ 
tive determination of tetryl and its degradation 
products by high pressure liquid chromatog¬ 
raphy”, J. Chromatogr., Vol. 114, 1975, p. 
261. 

(4) Meier, E. P., Taft, L. G., Graffeo, A. P., 
and Stanford, T. B., “The determination of se¬ 
lected munitions and their degradation products 
using high performance liquid chromatog¬ 
raphy”, Proceedings of the 4th Joint Confer¬ 
ence on Sensing of Environmental Pollutants, 
1977, p.487. 


(5) Beveridge, A. D., Payton, S. F., Andette, 
R. J., Lambertus, A. J., and Shaddick, R. C., 
“Systematic analysis of explosive residues”, J. 
Forensic Sci., Vol. 20, 1975, p. 431. 

(6) Kaplan, M. A. and Zitrin, S., “Identification 
of post-explosive residues”, JAOAC, Vol. 60, 

1977, p.619. 

(7) Midkiff, C. R. and Washington, W. D., 
“Systematic approach to the detection of explo¬ 
sive residues. III. Commercial dynamite”, 
JAOAC, Vol. 57, 1974, p. 1092. 

(8) Midkiff, C. R. and Washington, W. D., 
“Systematic approach to the detection of ex¬ 
plosive residues. IV. Military explosives”, 
JAOAC, Vol. 59, 1976, p. 1357. 

(9) Parker, R. G., Stephenson, M. O., McOwen, 
J. M., and Cherolis, J. A., “Analysis of explo¬ 
sives and explosive residues. Part 1. Chemical 
tests”, J. Forensic Sci., Vol. 20, 1975, p. 133. 

(10) Parker, R. G., McOwen, J. M., and 
Cherolis, J. A., “Analysis of explosives and 
explosive residues. Part 2. Thin-layer chroma¬ 
tography”, J. Forensic Sci., Vol. 20, 1975, p. 
254. 

(11) Chrostowski, J. E., Holmes, R. N., and 
Rhen, B. W., “The collection and determina¬ 
tion of ethylene glycol dinitrate, nitroglycerin 
and trinitrotoluene explosive vapors”, J. 
Forensic Sci., Vol. 21, 1976, p. 611. 

(12) Vidrine, D. W., “Liquid Chromatography 
detection using FT-IR”, Fourier Infrared Spec¬ 
troscopy, Basile, L. J. and Ferraro, J. R., ed., 
Academic Press, New York, Vol. 2, 1979, 
p. 129. 

(13) Vidrine, D. W., “A practical real-time 
Fourier transform infrared detector for liquid 
chromatography”, Appl. Spectrosc., Vol. 32, 

1978, p.502. 

(14) Kuehl, D. and Griffiths, P. R., “Dual-beam 
Fourier transform infrared spectrophotome¬ 
ter”, Anal. Chem., Vol. 50, 1978, p. 418. 

(15) Vidrine, D. W., “Use of subtractive tech¬ 
niques in interpreting on-line FT-IR spectra of 
HPLC column eluates”, J. Chromatogr. Sci., 
Vol. 17, 1979, p.477. 


307 







































ANALYSIS OF SMOKELESS POWDERS 
USING UV/TEA DETECTION 


Edward C. Bender 
FBI Laboratory 


ABSTRACT. The analysis of smokeless powders or propellants have been of 
long interest to the forensic examiner. Smokeless powders contain not only explo¬ 
sives such as nitroglycerine and nitrocellulose but also stabilizers gelatinizers and 
their various decomposition products which are themally labile. High Performance 
Liquid Chromatography allows their accurate characterization and quantitation. 
By using tandem UV/TEA detectors these compounds can be analyzed in the low 
nanogram range which is a requirement for some forensic applications. Diphenyla- 
mine, 2-nitrodiphenylamine, N-nitrosodiphenylamine, nitroglycerine, 2,6-dini- 
trotoluene and 2,4-dinitrotoluene have been separated identified and their relative 
quantites used to characterize the gun powder. 


INTRODUCTION 

Smokeless powders consist mainly of nitrocellu¬ 
lose. The burning rate of the propellants are ad¬ 
justed by varying the size and shape (ball, disk, 
cylinder), or by the addition of chemical modifiers 
and stabilizers. These compounds are what are of 
interest here. Gunpowders are grouped into three 
basic categories-single, double, and triple base. 
Single base powders consist mainly of nitrocellu¬ 
lose (NC). The addition of nitroglycerin (NG) to 
the nitrocellulose makes the propellant double 
base. A powder containing NG, NC and nitrogua- 
nidine salts is classified as triple base. These are 
used in rockets and military ordinance. 

Seven major constituents of smokeless powder 
were separated and identified. They are diphenyla- 
mine (DPA), 2-nitrodiphenylamine, 2,6 dinitro- 
toluene, 2,4 dinitrotoluene (DNT), nitroglycerin, 
N-nitrosodiphenylamine and n-butylphthalate. 
Diphenylamine and 2-nitrodiphenylamine are 
added to the nitrocellulose to stabilize it. They 
scavenge the nitric (nitrous) acid which is formed 
during the decomposition of NC. In turn the di- 
phenylamines are nitrated and nitrosated (N-ni- 
troso DPA). 2,4 DNT and its impurity 2,6 DNT 
are added to the propellant to modify the surface. 
The explosive oils, notably NG serve two func¬ 
tions — to increase the burning rate, and as a plas¬ 
ticizer or gelatinizer for the nitrocellulose. Dibutyl 
phthalate serves the latter purpose. 

The ultraviolet (UV) detector provided sensitiv¬ 
ity in the nanogram range for the compounds con¬ 


taining the aromatic moeity, but was less specific 
to the nitrate esters (NG). The Thermal Energy 
Analyzer (TEA) on the other hand was selective 
for nitroglycerin and N-nitroso DPA. The aro¬ 
matic nitro compounds showed poor sensitivity on 
the TEA because the 550°C pyrolysis temperature 
is not enough to effectively cleave the carbon-ni¬ 
trogen bond. 

In pre-blast situations or when comparing pow¬ 
ders for a possible common origin, the analysis is 
straightforward. An association with the manu¬ 
facturer and brand can usually be made if you 
have the standards. Post blast identification of 
powders is generally more difficult and sometimes 
impossible. After ignition or upon exposure to 
heat the smokeless powders shrink or melt, alter¬ 
ing their chemistry significantly. Also introduced 
into the sample are various contaminents ie. pyrol¬ 
ysis products, oils, plasticizers, and building mate¬ 
rials. In this case strict quantitation which is essen¬ 
tial in discriminating some brands is impossible. 
The analysis must be focused on identifying com¬ 
ponents unique to specific types of powders. This 
is where the TEA proves valuable. 

EXPERIMENTAL PROCEDURE 

Ten grains of each powder were extracted with 
five milliliters of methylene chloride. The extract 
was then passed through a silica Sep Pak followed 
by five milliliters of fresh solvent. The solution 
was then evaporated to half its volume with a ni- 


309 


trogen stream. This solution was then injected into 
the HPLC. 

The HPLC system consisted of two Waters 
6000A pumps and a U6K injector fitted with a 10 
ul loop. A Kratos 770 variable wavelength detec¬ 
tor in line with a Thermal energy analyzer, manu¬ 


factured by Thermal Electron were used to mon¬ 
itor the eluting stream. The UV detector was set 
at 254nm. and a pyrolysis temperature of 550°C 
was maintained on the TEA. The eluent was sev¬ 
enty percent isoostance in methylene chloride at a 
flow rate of two milliliters per minute. 


1 1 5 




5 1 




1 



Figure 1. UV response Hercules disk powders 1. DPA, 2. 2-nitro DPA, 3. 2,6 DNT, 4. 2,4DNT 5. NG, 6. N-nitroso DPA, 
7. Unknown, 8. DBP 


310 















































The first propellants analyzed were disk shaped 
powders from the Hercules Powder Company. 
(Figure 1) They were Red Dot, Herco, Unique, 
Bullseye and 2400. Their are similarities in the 
Hercules line notably the presence of the four 
compounds DPA, 2-nitro DPA, NG, N-nitroso 
DPA. Only two contain 2,4 DNT (Herco, 


Unique). The relative quantities of the major com¬ 
ponents and the presence or absence of minor 
components allow the easy discrimination of each 
of these powders. The TEA responded only to ni¬ 
troglycerin and the n-nitrosodiphenylamine and 
added little information to the UV chromatogram 
(See Figure 2). Physical diameter, thickness, and 




Figure 2. TEA response Hercules disk powders 5. NG, 6. N-nitroso DPA 


311 











the perforation or lack of perforations will add 
further clarification to the identity of the powder. 
It should be noted that all the Hercules flake pow¬ 
ders are double-base; this is not the case for other 
manufacturers. 


The disk powders in the Dupont series varied 
greatly. The propellant designated “PB” proved 
to be single-base with large amounts of 2,4 DNT 
and DPA. (see Figure 3). The TEA showed the ab¬ 
sence of NG with only N-nitrosodiphenylamine 


4 




Figure 3. Dupont disk powder 1. DPA, 2. 2-nitro DPA, 4. 2,4 DNT, 6. N-nitroso DPA, 8. DPA 


312 










appearing in the chromatogram. Conversely Du¬ 
pont 700-X was shown to be double-base. It also 
showed an abundance of 2,4 DNT and DPA but 
had a significant amount of NG. (see Figure 4). It 
was later shown that the “X” designation in a Du¬ 


pont powder indicates the presence of NG. Also 
large amounts of 2,4 DNT in a disk shaped pow¬ 
der would be significant in discerning a Hercules 
from a Dupont propellant. 

Two other flaked powders were examined— 




Figure 4. Dupont disk powder 1. DPA, 2. 2-nitro DPA, 4. 2,4 DNT, 5. NG, 6. N-nitroso DPA 


313 



















Nike and Norma 2020. The Nike powder was 
shown to be double-base. It contained DPA, 2-ni- 
tro DPA and a large amount of N-nitroso-DPA. 
(Figure 5). This is probably due to the age of the 
powder. Most of the DPA originally present has 
decomposed to its nitroso deservative. The Norma 
powder showed only NG present in significant 
amounts. 

The ball powders are exclusively double base. 
Physically they appear as small balls, flattened 
balls or a mixture of both. Examples of ball pow¬ 
ders are two manufactured for the Hodgdon Pow¬ 
der company—H-l 10 and H-BLC-2. These pow¬ 


ders contain the same components the differences 
being in their relative quantities. The greatest dis¬ 
parity in the brands lies in the large amount of the 
unknown compound at retention time 23.07 in 
H-BLC-2 and a considerably smaller amount in 
H-l 10. (see Figure 6). Another ball powder Win¬ 
chester Western WW-296 is very similar to the 
Hodgden powders (Figure 7). Winchester Western 
252-AA shows the presence of a large amount of 
an unknown compound at retention time 26.6 
which distinguishes the AA powders from all oth¬ 
ers. 

The Dupont IMR (improved military rifle) sin- 




Figure 5. UV response Nike and Norma disk powder 1. DPA, 2. 2-nitro DPA, 3. 2,6 DNT, 4. 2,4 DNT, 5. NG, 6. N-nitroso 
DPA, 8. DBP 


314 





























Figure 6. UV response Flogdon ball powders 1. DPA, 2. 2-nitro DPA, 3. 2,6 DNT, 4. 2,4DNT, 5. NG, 6. N-nitrosoDPA 


gle base series is typefied by the large amount of 
2,4 DNT. (Figure 8). Present in small quantities 
are DPA, 2-nitro DPA, the 2,4 impurity 2,6 
DNT, N-Nitroso DPA and n-butyl phthalate. 
The relative ratios of these lesser components 
prove to be the key in distinguishing chemically 
the members of the IMR series, (measuring the 
length of the cylinder is a more definitive tech¬ 


nique if the powder is intact). The TEA shows a 
large response for the nitrosamine and gives a 
small peak for 2,6 DNT. Herter’s 100 another cy- 
clindrical single base powder shows large amounts 
of DPA and very little 2,4 DNT contrary to the 
IMR series. (Figure 9) The TEA shows again a 
large response to N-ntroso DPA but another com¬ 
pound of unknown identity is revealed. 





Figure 7. UV response Winchester Western 296 and 252AA 1. DPA, 2. 2-nitro DPA, 3. 2,6DNT, 4. 2,4 DNT, 5. NG, 6. N-ni- 
troso DPA 


315 





























































As was shown most cylindrical propellants are 
single base, their is however, a notable exception 
the Hercules Reloader line. For example, RL-7 
contains DPA and its decomposition product, 
N-Nitroso-DPA lesser quantities of 2-nitro DPA 
and 2,4 DNT but is also has NG, making it double 
base. The TEA chromatogram shows NG, the ni- 
trosoamine plus what is apparently EGDN. 


6 



In order to study post blast propellants pipe 
bombs were constructed. They were initiated with 
safety fuze. The pipe fragments were collected and 
were brushed off to remove any residual powder. 
The fragments were then extracted with dichloro- 
methane and injected into HPLC system. In this 
analysis the TEA proved to be very valuable be¬ 
cause of the presence of contamination. Winches- 


4 



Figure 8. Dupont IMR—3031 UV and TEA response 1. DPA, 2. 2-nitro DPA, 3. 2,6 DNT, 4. 2,4 DNT, 6. N-nitroso DPA, 
8. DBP 


316 



















6 



1 



Figure 9. Herters 100 UV and TEA response 1. DPA, 2. 2-nitro DPA, 6. N-nitroso DPA 


317 















































ter Western WW-760 was one of the powders 
used. On the UV chromatogram a large number of 
compounds were detected (Figure 11). (Probably 
originating from thread cutting oil) including 
2,4DNT. None of the other common components 
in smokeless powder were found due to the con¬ 
tamination. The TEA was able to pick out NG and 
N-nitroso DPA which also implies DPA was pres¬ 
ent. From this information it could be concluded 
that the main charge was probably a ball powder. 
A single-base powder IMR-3031 was examined in 


5 



the same way. The only compound found was 2,4 
DNT as would be expected. (Figure 12). The TEA 
showed no response for NG. 

HPLC with UV/TEA detection proved to be a 
valuable technique for the analysis of smokeless 
propellants in forensic applications. Not only is it 
possible to determine the brand of powder and to 
do batch associations, but many inferences can be 
made in post blast situations where none of the 
powder remains. 


i 



Figure 10. Hercules RL-7 UV and TEA response 1. DPA, 2. 2-nitro DPA, 4. 2,4 DNT, 5. NG, 6. N-nitroso DPA 


318 



































5 



Figure 11. Exploded Winchester Western 760 UV and TEA response 4. 2,4 DNT, 5. NG, 6. N-nitrosoDPA 


319 






































Figure 12. Exploded IMR-3031 UV response 


320 





DETECTION OF EXPLOSIVE RESIDUES BY MICROBORE HPLC 

Jeff Bowermaster and Harold M. McNair 

Department of Chemistry 
Virginia Polytechnic Institute and State University 
Blacksburg, VA 24061 


ABSTRACT. Microbore (1 mm I.D.) HPLC columns have aroused considerable 
interest of chromatographic workers. Considerable confusion exists over their re¬ 
ported claims of better sensitivity and better resolution. These points are clarified 
by specifying those chromatographic conditions which must be controlled for valid 
comparisons. Details for packing microbore columns are provided and their ap¬ 
plication to the analysis of traces of explosive residues is shown. 


INTRODUCTION 

In the recent rise in popularity of 1mm I.D. 
packed LC columns (1,2,3), confusion has existed 
concerning their advantages over conventional 
bore (4-4.6 mm I.D.) packed LC columns. The re¬ 
duced diameter of these microbore columns re¬ 
sults in a clear-cut solvent savings (4). The very 
low flow rates (10-100 /^l/min) mean easy interfac¬ 
ing of microbore HPLC systems and spectro¬ 
scopic detectors such as MS, FTIR and NMR. 
There is, however, no reason to expect higher res¬ 
olution or improved speed from microbore col¬ 
umns as these parameters are not governed by the 
column diameter, but, rather primarily by the di¬ 
ameter of the particles used to pack the column 
(5). Columns are routinely packed in our lab in 
longer lengths than those reported for convention¬ 
al bore columns resulting in individual columns 
delivering very high resolution. However, conven¬ 
tional bore columns can simply be coupled pro¬ 
ducing the same high plate counts (6). 

Microbore columns have the potential to deliver 
improvements in sensitivity, but only in cases 
where particular criteria are satisfied. “Column 
amplification’’ (7) results when the volume of sol¬ 
vent mobile phase containing a fixed amount of 
sample is reduced. This reduction in solvent vol¬ 
ume is achieved by reducing the column diameter. 
The prerequisites needed in order to realize in¬ 
creased sensitivity are: 

1. The same volume of sample must be applied 
to both conventional bore and microbore col¬ 
umns. 

2. The same mass applied to both columns 
must be below the mass overload of both columns. 

3. The geometry of the detector cell must be 


identical in both cases. 

We will now consider each of these points in de¬ 
tail. 

1. The concomitant reduction in the volume of 
the peak with the reduction in column diameter 
means that unless a weak sample solvent is em¬ 
ployed (8) (so that sample components in a large 
volume condense at the head of the column), the 
bandspreading caused by 10/jl injection onto a 
microbore column will seriously reduce observed 
efficiency. However with weak sample solvent 
trapping, 25 p<l has been injected onto a microbore 
column in our lab with no loss in resolution. (9). 

2. Column overload occurs when more than 0.1 
mg of sample per gram of sorbent is injected on a 
column, and is characterized by skewed peaks. In 
most cases, compounds analyzed by LC have ex¬ 
tinction coefficients high enough that sample 
charges do not exceed column overload concentra¬ 
tions. However, this is not always the case. The re¬ 
duction in sample capacity parallels the reduction 
in solvent consumption in microbore columns. A 
typical microbore column has 1 /20th the 
cross-sectional area of a 4.6 mm I.D. column. 
Thus, for equal column lengths and equal linear 
mobile phase velocities the microbore will use 
1 /20th the mobile phase volume, and accommo¬ 
date only 1 /20th the sample mass. A conventional 
bore and microbore column both operated at col¬ 
umn capacity will deliver exactly the same sample 
concentrations to a detector cell resulting in iden¬ 
tical sensitivities for both systems (assuming the 
same detector is employed). However, in cases 
where only a limited amount of sample is available 
(such as forensic applications and some areas of 
biomedical research) the microbore system will in- 


321 


deed deliver a higher concentration to the detector 
cell for a fixed sample mass provided this mass 
does not overload the column. 

3. The reduced peak volumes from microbore 
columns may require a reduction in the detector 
cell volume in order to reduce extra column band 
broadening and maintain resolution. If the path 
length of the cell is reduced, so is the sensitivity. If 
sensitivity is the goal, some sacrifice in resolution 
must be made in order to maintain sensitivity. 
Peak width, expressed as the square root of the 
variance (o) is 

(1 +K')Vo 

o = - 

v/~N 

where k ' is the capacity factor, Vo is the void vol¬ 
ume and N is the number of theoretical plates. It 
has been shown (9) that if the square root of the 
variance of the peak and the volume of the detec¬ 
tor cell are equal, there will be less than a 5% in¬ 
crease in the observed peak width caused by the 
static volume of the cell at low flow rates. Given a 
well packed 10 micron, 50 cm microbore column 
producing 25,000 theoretical plates, conventional 
8 /jl volume detector cells can be used as long as the 
k ' exceeds 4, with less than a 5% reduction in res¬ 
olution caused by this large cell volume. This 
means that, given a tight, low volume connection 
to the cell, many conventional detectors can be 
used with microbore columns. Depending upon 
the complexity and concentration of species pres¬ 
ent in a sample, detector cells can be chosen to 
provide either high resolution or high sensitivity. 

This paper will demonstrate by the use of micro¬ 
bore columns in the analysis of trace levels of ex¬ 
plosives on post-explosion debris. 

EXPERIMENTAL 

A MACS (Micro-Analytical Chromatographic 
System, EM Science, Gibbstown, NJ) was used 
for all analyses. This includes the MACS Model 
500 0.5/ul internal loop injector connected by a 3.6 
cm x 0.010" I.D. coupling to a microbore column. 
The MACS Model 700 variable wavelength UV 
detector was used with either the 0.5/ul or 8.0/jl de¬ 
tector cells (path lengths of 1 and 10 mm, respec¬ 
tively. 

The column terminates directly at the detector 
cell. The volume between the column outlet and 
the optical path was less than 1/d in the 0.5/d cell, 
but the 8 .0/d cell has a 4/d volume prior to the en¬ 
trance of the light path. This was removed by in¬ 
serting a 0.010" I.D. teflon capillary tube in this 


volume, reducing it to < 1/A Chromatograms run 
before and after this procedure showed both an in¬ 
crease in sensitivity and resolution (1.5-2 x ) using 
the cell with the smaller inlet volume. 

COLUMNS 

A 1 mm x 50 cm microbore column packed with 
LiChrosorb RP-18, l\x ( E. Merck, Darmstadt, 
Germany) was prepared using slurry packing with 
95/5 CCI 4 /CH 3 OH (5 ml slurry solvent to 0.32 g 
sorbent) driven with MeOH at 10,000 psi. Tubing 
(1/16 O.D. x 1 mm I.D.) was manually polished 
on the inside using string and abrasive. This proce¬ 
dure is essential to obtaining good columns and 
deserves some comment. 

Glass has been shown (10) to be the best surface 
for packed capillary (0.35 mm I.D.) LC columns 
and it is believed the smoothness of the glass is re¬ 
sponsible for its high performance. Glass-lined 
microbore columns are available commercially 
(Whatman, Clifton, NJ). Homemade glass-lined 
stainless steel columns have several disadvantages 
over polished stainless steel columns, including: 

1. Their 1/8" O.D. requires the use of bulky 
endfittings, making direct connection to the detec¬ 
tor cells impossible. An additional outlet transfer 
tube must be used, which at low flow velocities 
does not degrade performance, but does add to 
the plate height at high flow rates. 

2. They are inflexible, making connections to 
instrumentation more difficult than 1/16" micro¬ 
bore columns. 

3. The high cost ($25 as opposed to $2 for 
1/16" stainless steel tubing) of the column blank. 

4. The imprecision in end fitting installation 
coupled with not knowing if the glass has been 
crushed when seating the ferrule. 

Certainly good columns can be made with 
glass-lined stainless steel tubing. The polishing 
procedure on 1/16" stainless steel tubing makes 
use of glass-lined tubing unnecessary, avoiding 
the problems above. 

POLISHING PROCEDURE 

The polishing procedure involves clamping the 
1/16" column in place using two vices, protecting 
the tubing from crushing by surrounding it with 
thickwalled rubber tubing. A doubled strand of 
thin thread is pulled through the tube with a vac¬ 
uum pump. A thicker thread (i.e. button and car¬ 
pet thread) is pulled through as a loop, followed 
by this thicker loop pulling as much thread as can 
be comfortably pulled without breaking the 


322 



threads. White polishing compound (E. I. 
DuPont de Nemours and Co., Wilmington, DE), 
commonly used to remove oxidized paint from 
automobiles, is applied to the threads and polish¬ 
ing proceeds by pulling the coated strings back 
and forth for 5-10 minutes with the generation of 
considerable amount of heat. A clean thread bun¬ 
dle is inserted and the process is repeated, fol¬ 
lowed by a final bundle which is not coated with 
abrasive and is used to buff the inside of the tube 
and remove traces of polishing compound. Visual 
inspection of the interior of the tube reveals elimi¬ 
nation of interior surface roughness. This rough¬ 
ness was the cause of the early failure of many 
commercial microbore columns (void formation, 
loss in efficiency) as well as their low original per¬ 
formance. Reduced plate heights of 2 are usually 
obtained using polished tubing. 



TIME (MINUTES) 

Figure 1. Sensitivity in Microbore HPLC 


SAMPLES 

TNT, RDX and PETN as well as simulated ex¬ 
plosion residue samples were obtained through the 
FBI Academy, Quantico, VA. Explosion wreck¬ 
age was generated by blowing up sections of a gal¬ 
vanized steel trash can, and since these tests took 
place outside, samples collected afterwards were 
encrusted with varying amounts of mud and 
rocks. Extraction was performed by spraying 
these irregular shapes with 25 ml of acetonitrile 
and collecting the run-off in 600 ml beakers. Ali¬ 
quots were either directly injected or concentrated 
10 x by blowing down with nitrogen prior to in¬ 
jection. 

RESULTS 

Conditions for all analyses is shown in Table 1. 
Figure 1A shows explosive standards injected at 



B. 10 mm 

for Detector Cells of Different Pathlengths. 


323 










































TABLE 1 


Column 

Sorbent 

Solvent 

Flow Rate 

Pressure 

Detector 

Sensitivity 

Time Constant 

Temperature 


Conditions 

50 cm X 1 mm ID 

LiChrosorb RP-18, 7u 

2:1 Acetonitrile: Water 

50 ul/min 

800 PS1 

UV @ 210 nm 

0.01 Absorbance Units 

1 second 

Ambient (22C) 


levels of 8 ng/ml and 1 ng/ml, giving a detection 
limit of 100-500 pg in the 1 mm pathlength 0.5 pi 
detector cell. By switching to the 10 mm path- 
length 8.0pl cells (Figure IB), peak heights are in¬ 
creased, but so is baseline noise. The longer path- 
length provides greater sample sensitivity but is 
also more sensitive to small temperature fluctua¬ 
tions which causes refractive index changes result¬ 
ing in increased noise. The frequency distribution 
of this baseline noise is typically lower than the 
frequency spectrum of eluting peaks. In principle, 


it should be possible to filter out the low frequency 
noise but the procedure would require the use of 
complex digital filtering techniques as opposed to 
the simple analog low pass filter available on the 
MACS. It should also be possible to reduce the 
noise by carefully matching the temperature of the 
column and the cells, thus reducing changes in the 
refractive index of the solvent as if traverses the 
light path. In the present case, absolute peak 
height is improved 8 times going to the 8 pi volume 
cells. Depending upon which definition of noise is 
used, the noise increased 2-3 times, resulting in an 
overall improvement in sensitivity of 3-4 times. 
Resolution was reduced, going from 32,000 plates 
with the 0.5pl cells down to 22,000 plates with the 
8.0pl cells (measured on RDX, Peak #3). 

Figures 2-4 demonstrate the sensitivity and res¬ 
olution of microbore HPLC in the analysis of 
trace explosive residues. 

Figure 2 shows that the concentration of PETN 
recovered from the post blast residue was twice the 



Figure 2. PETN Analysis at 210 and 240 nm. 


324 
































Figure 3. Analysis of TNT. A. Original Extract. B. 10X Concentration of Original Extract. 


8 ng/ml standard, meaning the total amount avail¬ 
able on the original sample was 200 fug. The peak 
in the explosive residue sample which eluted at the 
same time as the PETN standard showed the cor¬ 
rect absorption ratio at 210/240 nm, thus increas¬ 
ing the confidence that this peak was PETN. 

Figure 3 showed a more complex matrix for the 
TNT sample. Nevertheless, the microbore column 
was able to distinguish TNT from over 100 other 
peaks in the sample (only a part of the chromato¬ 
gram is shown). Ten-fold concentration of the ini¬ 
tial extract resulted in the baseline being off-scale 
during the elution of the TNT peak, but 
auto-zeroing just prior to the TNT’s elution (Fig¬ 
ure 3B) did reveal a peak at the proper retention 
time with ten times more height. 

Figure 4 shows the least definitive identifica¬ 
tion, that for RDX. It appeared as a shoulder on 
one peak, and, unfortunately, when run at other 
wavelengths the surrounding peaks obscured it. In 
this case, the use of more specific detectors (TEA 
(11), ECD (12), EC (13)) would have been needed 
for confirmation of this species. 


CONCLUSION 

Microbore HPLC provides sufficient sensitivity 
and resolution for the detection of trace explosive 
residues in real samples. Its advantages over con¬ 
ventional bore columns is that it uses less solvent 
and in the case of limited samples can provide in¬ 
creased sensitivity. 

ACKNOWLEDGEMENTS 

We thank E. Bender and Dr. D. Reutter for 
providing us with samples. We gratefully acknow¬ 
ledge financial support of this project by the Na¬ 
tional Aeronautics and Space Administration with 
grants NAG-1-246 and NAG-1-343. 


325 
























































ABSORBANCE 


.05- 


RDX 



0 10 20 
TIME (MINUTES) 


Figure 4. RDX Analysis 


326 


























REFERENCE 

1. R. P. W. Scott and P. Kucera (1979). Mode 
of operation and performance characteristics 
of microbore columns for use in liquid 
chromatography. J. Chromatogr. 
169: 51-72. 

2. R. P. W. Scott and P. Kucera (1979). Use of 
microbore columns for the separation of sub¬ 
stances of biological origin. J. Chromatogr. 
185: 27-41. 

3. R. P. W. Scott, P. Kucera and M. Munroe 
(1979). Use of microbore columns for rapid 
liquid chromatographic separations. J. 
Chromatogr. 186: 475-487. 

4. J. H. Knox (1980). Theoretical aspects of LC 
with packed and open small bore columns. 
J. Chromatogr. Sci. 18: 453-461. 

5. G. Giochon (1981). Conventional packed col¬ 
umns vs. packed or open tubular microcol¬ 
umns in liquid chromatography. Anal. Chem. 
53: 1318-1325. 

6. J. C. Kraak, H. Poppe and F. Smedes (1976). 
Construction of columns for liquid chromato¬ 
graphy with very large plate numbers. J. 
Chromatogr. 122: 147-158. 

7. P. B. Hamilton (1966). Ion exchange chrom¬ 
atography of amino acids in advances in 
chromatography, J. C. Giddings and R. A. 
Keller, ed. Marcel Dekker, New York, p. 44. 

8. M. Broquaire and P. R. Guinebault (1981). 


Large volume injection of biological samples 
dissolved in a non-eluting solvent: a way to 
increase sensitivity and a means of automating 
drug determination using HPLC. J. Liq. 
Chromatography 4(11): 2039-2061. 

9. J. Bowermaster and H. M. McNair (1983). 
Microbore HPLC columns: Speed efficiency, 
sensitivity and temperature programming. 
Proceedings of the fifth international sympo¬ 
sium on capillary chromatography. Elsevier, 
Amsterdam, p. 725-734. 

10. T. Takerichi and D. Ishii (1980). Ultra-micro 
high performance liquid chromatography. J. 
Chromatogr. 190: 150-155. 

11. D. H. Fine, W. C. Yu, E. V. Goff, E. Bender 
and D. Reutter (1983). Picogram analyses of 
explosive residues using the TEA analyzer. 
Submitted to J. Forensic. Sci. 

12. A. DeKok, R. B. Geerdink and V. A. Th. 
Brinkman (1982). Improved interface for liq¬ 
uid chromatography-electron-capture detec¬ 
tor coupling. I. J. Chromatogr. 
252: 101-111. 

13. K. Bra tin, P. T. Kissinger, R. C. Briner and 
C. S. Bruntlett (1981). Determination of ni- 
troaromatic, nitramine and nitrate ester ex¬ 
plosive compounding explosive mixtures and 
gunshot residues by liquid chromatography 
and reductive electrochemical detection. 
Anal. Chim. Acta. 130: 295-311. 


327 









































































DETERMINATION OF NITRATE ESTERS, NITRAMINES, 
NITROAROMATICS, AND THEIR METABOLITES IN 
BIOLOGICAL FLUIDS AND WASTEWATER BY GAS AND 
LIQUID CHROMATOGRAPHY WITH A NITRO/NITROSO 

SPECIFIC DETECTOR 

Yu, W. c., Goff. E. U. 

Thermo Electron Corporation 
101 First Avenue 
Waltham, MA 02254 

Fine, D. H. 

New England Institute for Life Sciences 
125 Second Avenue 
Waltham, MA 02254 

ABSTRACT. As a consequence of work with cardiovasodilators, the capability 
now exists to evaluate the potential occupational hazard associated with human ex¬ 
posure to explosives via skin contact and/or vapor inhalation in biological fluids. 
A technique using the TEA® Analyzer interfaced to a gas chromatograph (GC) or 
a high-performance liquid chromatograph (HPLC) is described for the trace level 
determination of nitroglycerin, pentaerythritol tetranitrate, and their metabolites 
in blood. The method developed is capable of detecting 0.1 nanogram of each of 
the nitrate esters. The precision of the HPLC-TEA method at 1 ng/ml (ppb) level 
was established to be 7.4% and 5.7% relative standard deviation (RSD) for nitro¬ 
glycerin and pentaerythritol tetranitrate, respectively. Analytical methodologies 
developed for the detection of cyclotrimethylenetrinitramine (RDX), trinitroto¬ 
luene (TNT), cyclotetramethylene tetranitramine (HMX) in biological matrix and 
wastewater effluents are also discussed. 

INTRODUCTION 

The manufacture of explosives is an important 
industry related to national defense, commerce, 
industrial blasting and demolition. According to 
the 1976 estimates by the National Institute for 
Occupational Safety and Health (NIOSH), ap¬ 
proximately 8000 workers in the U.S. dynamite in¬ 
dustry are exposed to nitroglycerin (NG) either 
alone or in combination with ethylene glycol dini¬ 
trate (EGDN). During 1981, the Bureau of Mines 
estimated that 4.3 billion pounds of explosives 
were manufactured in the United States, 65% of 
which were consumed in the coal mining industry. 

In the pharmaceutical industry, nitrate esters such 
as nitroglycerin, pentaerythritol tetranitrate 
(PETN) and isosorbide dinitrate (ISDN) are fre¬ 
quently used as coronary vasodilators for the 
therapeutic treatment of angina pectoris and acute 


myocardial infarction. Nitroglycerin oral tablets, 
for example, have been prescribed for the fast re¬ 
lief of acute anginal pain because of its rapid onset 
effect on the dilatation of blood vessels. 

Occupational exposure can either be through 
vapor inhalation or skin absorption, or a combi¬ 
nation of both (Bishop et al. 1981; Gotell, 1976; 
Hogstedt and Stahl, 1980; Hogstedt and Davids- 
son, 1980). For an eight hour time-weighted aver¬ 
age exposure of about 1 mg/m 3 EGDN in the air, 
it is estimated that a blood level of a maximum 2 
ng/mL EGDN would be observed (Gotell, 1976). 
However, the major route of exposure is through 
skin contact, accounting for over ninety percent. 
Historically, the typical symptoms of exposure to 
explosives are headaches, dizziness, nausea, heart 
palpitations and in severe cases, death may occur 
(Carmichael and Lieben, 1963; Lund et al. 1968; 


329 


Morikawa et al. 1967). In the environmental area, 
effluents from the operation of munitions manu¬ 
facturing could lead to the contamination of sea, 
ground and surface water, soils and sediments, all 
of which may pose a potential health hazard. Tri¬ 
nitrotoluene (TNT) has been identified in the 
ground water after leaching from disposal sites 
(Pereira et al. 1979). Over thirty (30) nitroaro- 
matic compounds were identified in the waste- 
water effluent generated in the manufacture of 
TNT (Spanggord et al. 1982). NG and degradation 
products were determined in wastewaters (Chand¬ 
ler et al. 1974), and EGDN was identified in drink¬ 
ing water (Fan et al. 1978). 

The toxicity and toxic effects of TNT are 
well-documented (Crawford, 1954; Djerassi and 
Vitany, 1975: McConnell and Flinn, 1946; Mor¬ 
ton et al. 1976) and its occupational exposure has 
been reported to occur by inhalation, skin absorp¬ 
tion, and injestion. Tetryl, a nitroaromatic explo¬ 
sive, has been tested to be mutagenic in three mi¬ 
crobial test systems (Whong et al. 1980). The toxic 
effects of RDX in humans has been associated 
with epileptiform seizures (Barsotti and Crotti, 
1949; Kaplan etal. 1965). 

In light of worker exposure and the potential 
health hazard associated with it, NIOSH in 1976 
proposed a ceiling concentration of 0.1 mg/m 1 for 
NG and EGDN for a 20 minute sampling period. 
The U.S. Department of the Navy’s Bureau of 
Medicine and Surgery (BUMED) has identified 
five constituents of ordnance-disposal waste— 
ammonium picrate, picramic acid, propylene gly¬ 
col dinitrate, RDX, and TNT—as potential con¬ 
taminants of drinking water, and has established a 
target interim maximal contaminant level for 
drinking water. (National Academy Press, 1982). 

To assess the occupational exposure of these 
compounds in environmental and biological ma¬ 
trices, it is necessary to develop viable analytical 
methodologies and sensitive instrumentation. The 
TEA analyzer has been demonstrated to be a sen¬ 
sitive and selective detector for nitro-based com¬ 
pounds (Goff et al. 1983); LaFleur and Morriseau 
1980; Yu and Goff, 1983). Its application for the 
explosives in post-blast debris, post-blast air sam¬ 
ple, and handswabs was already presented in an 
earlier report (Fine et al. 1983). In this paper, we 
describe its application in the environmental and 
biological areas. 


EXPERIMENTAL PROCEDURE 
Reagents 

All solvents were distilled-in—glass grade (Bur¬ 
dick and Jackson). Glyceryl 1,2-dinitrate and 
1,3-dinitrate (1,2-GDN and 1,3-GDN), glyceryl 
2-mononitrate (2-GMN) and glyceryl 1-mononi¬ 
trate (1-GMN) were synthesized by the method of 
Dunstan et al (1965). Isosorbide 2-mononitrate 
and 5-mononitrate (2-ISMN and 5-ISMN) were 
obtained from Dr. John Markis, Beth Israel Hos¬ 
pital, MA. Sep-PAK Q 8 cartridges (Waters Asso¬ 
ciates) and Miller-SR filters (Millipore Corpora¬ 
tion) were used for sample preparation. 

Equipment 

The liquid chromatograph (HPLC) was con¬ 
structed with an Altex Model 110 solvent delivery 
pump (Altex Scientific Inc.) and a U6K universal 
injector (Waters Associates). A 10 um, 3.9 mm 
i.d. x 30 cm uBondapak CN column (Waters As¬ 
sociates) was used for the separation of isosorbide 
dinitrate, glyceryl trinitrate, and pentaerythritol 
tetranitrate, with a mobile phase consisting of 
iso-octane-methylene chloride-methanol (75: 
20:5) and at a flow rate of 1.5 ml/min. For the 
separation of the vasodilators and their respective 
metabolites a 10 um 4.6 mm i.d. x 25 cm Ultrasil 
NH 2 column (Altex Scientific Inc.) was used, with 
a mobile phase consisting of iso-octane-methy¬ 
lene chloride-methanol (80:13:7) at a flow rate of 
2 ml/min. For the analysis of RDX and HMX, the 
cyano column was used, with a mobile phase con¬ 
sisting of isooctane-methylene chloride-methanol 
(60:30:10) at a flow rate of 1.5 ml/min. The 
amount injected onto HPLC was 10 uL. 

The detector was a TEA Model 510 analyzer 
(Thermo Electron Corporation) operating in the 
LC mode. The catalytic pyrolyzer temperature 
was maintained at 550 °C. The carrier gas was ni¬ 
trogen at a flow rate of 20 ml/min. Oxygen was 
maintained at a flow rate of 5 ml/min. The reac¬ 
tion chamber vacuum was 1.8 mm Hg. The cryo¬ 
genic traps were maintained at -78°C with an 
ethanol-solid carbon dioxide slush bath. 

The conditions for gas chromatograph—Ther¬ 
mal Energy Analyzer (GC-TEA) operation has 
already been discussed by Fine et al. (1983) in an 
earlier report of this symposium. 

Sample Preparation 

A. Nitrate esters in plasma 

Five ml of fresh frozen plasma (sampled imme¬ 
diately after thawing) were pipetted into culture 


330 


tubes and fortified with glyceryl trinitrate, isosor- 
bide dinitrate, pentaerythritol tetranitrate, and se¬ 
lected lower nitrates at various levels. The samples 
were extracted with ethyl acetate (8 ml) and centri¬ 
fuged to separate the two phases. The supernatant 
was transferred to a clean culture tube, and the 
plasma was re-extracted with 2 x 8 ml ethyl ace¬ 
tate. The pooled extract was loaded onto a 
Sep-Pak Cig cartridge and clarified by a 0.5 mi¬ 
cron Millex-SR filter. After concentration under a 
gentle stream of nitrogen at 35 °C to 0.5 milliliter, 
the filtrate was transferred to a 1 ml vial and fur¬ 
ther concentrated to approximately two hundred 
microliters. Aliquots of the concentrated extract 
were injected on HPLC-TEA. 

B. RDX in plasma 

Five ml of plasma was fortified with RDX at the 
5 ppb level, extracted with 16 ml of methylene 
chloride and pentane (1:1), clarified by filtration 
through a SEP-PAK Ci 8 cartridge and a 
Millex-SR filter, concentrated under N 2 to 0.2 ml, 
and analyzed by injecting 25 ul onto HPLC-TEA. 

C. Wastewater effluent samples 

Ten ml of sample was loaded onto a preptube 
Type 117 (Thermo Electron Corporation) which 
was prewet with ten ml dichloromethane (DCM). 
The sample was eluted with 8 x 10 ml DCM into a 
Kuderna-Danish evaporator. The eluant was 
evaporated at 54 °C to 2 ml. Aliquot of the con¬ 
centrated extract was injected onto HPLC-TEA 
and GC-TEA. 

RESULTS AND DISCUSSION 
Chromatography 

The separation of the nitrate esters was achieved 
on a uBondapak CN column using isocratic condi¬ 
tions, as shown in Figure 1. The compounds were 
1 -ISDN, 11 ng; 2-NG, 5ng; and 3-PETN, 11 ng. 
When the column functionality was changed to 
the amino bonded phase, the lower nitrate me¬ 
tabolites of NG, ISDN, and PETN were resolved, 
as shown in Figures 2 and 3. 

Human Plasma Samples 

The half-lifes of the nitrate esters in the human 
blood stream are relatively short (Armstrong et el. 
1979). They are rapidly degraded to the lower ni¬ 
trate metabolites (Davidson et al. 1971; DiCarlo et 
al. 1968) which are more stable. To assess the oc¬ 
cupational exposure, it would then be prudent to 
monitor the parent compounds, as well as the ni¬ 
trated metabolites. Table 1 shows the recovery of 


the nitrate esters and selected nitrated metabolites 
from human plasma at fortification levels ranging 
from 1 ng/ml to 80 ng/ml. Procedures for the 
analysis of the nitro-based vasodilators, at the 
blood level of 0.1-0.2 ng/ml, are now routine 
(Maddock et al. 1983; Spanggord and Keck, 1980; 
Yu and Goff, 1983). 



TIME (minutes) 

Figure 1. HPLC-TEA Chromatogram of Nitrate Esters: (1) 
isosorbide dinitrate, 11 ng (2) glyceryl trinitrate, 5 ng (3) 
pentaerythritol tetranitrate, 11 ng. 


331 












DETECTOR RESPONSE (arbitrary units) 



TIME (minutes) 



TIME (minutes) 


Figure 2. A. HPLC-TEA Chromatogram of Glyceryl Trinitrate and Metabolites: (1) glyceryl trinitrate, 2.5 ng (2) glyceryl 
1,3-dinitrate, 3.7 ng (3) glyceryl 1,2-dinitrate, 0.7 ng (4) glyceryl 2-mononitrate, 2.2 ng (5) glyceryl 1-mononitrate, 4.4 ng 
B. HPLC-TEA Chromatogram of Isosorbide Dinitrate and Metabolites: (1) isosorbide dinitrate, 4 ng (2) isosorbide 2-mononi¬ 
trate, 10 ng (3) isosorbide 5-mononitrate, 10 ng. 


332 





























A. 


B. 



TIME (minutes) TIME (minutes) 


Figure 3. HPLC-TEA Analysis of Pentaerythritol Tetranitrate: A. Reference Standards (1) pentaerythritol tetranitrate, 5 ng (2) 
pentaerythritol trinitrate, 4.6 ng (3) pentaerythritol dinitrate, 13.6 ng B. plasma fortified with PETN at 10 ng/ml level. 


333 






















Table 1. RECOVERY OF NITRATE ESTERS AND NITRATED METABOLITES FROM PLASMA MEAN RECOVERY 
(%, ± S.D., n = 4) 
ng/ml 


added 

NG 

ISDN 

PETN 

1,2 GDN* 

1-GMN* 

PETRIN* 

PEDN* 

2-ISMN* 

1 

54 ± 4 

76 ± 6 

67 ± 4 

_ 

_ 

— 

— 

— 

5 

65 + 7 

62 ± 4 

63 ± 4 

91+5 

91 ± 15 

61 ± 4 

63 ± 4 

85 ± 6 

10 

77 + 6 

80 ± 5 

67 ± 2 

— 

— 

— 

— 

— 

20 

74 ± 7 

69 ± 5 

71 ± 1 

86 ± 3 

60 ± 13 

66 ± 4 

60 ± 2 

92 ± 12 

40 

82 ± 9 

80 ± 5 

63 ± 4 

— 

— 

— 

— 

— 

80 

81 ± 5 

65 ± 5 

72 ± 4 

— 

— 

— 

— 

— 


* Recoveries on these compounds were conducted at 5 ng/ml and 20 ng/ml only. 
PETRIN—Pentaerythritol trinitrate 
PEDN—Pentaerythritol dinitrate 


In the experiments recently conducted by Twi- 
bell et al. (1982), NG could still be detected in a 
person’s hands more than 20 hours after he had 
handled commercial explosives, even though his 
hands had been washed several times. Because of 
possible occupational hazards, there is a need to 
detect military explosives in human blood. This 
capability was explored with PETN and RDX. 
The chromatogram, shown in Figure 3, represents 
a plasma sample fortified with PETN at the 10 
ng/ml level, and in Figure 4 for a 5 ng/ml RDX 
plasma spike. Because of the specificity of the 
TEA analyzer, interferences normally encount¬ 
ered in other detectors due to components such as 
proteins, glucuronides, and lipids present in 
plasma or blood do not represent a problem with 
the method. 

Wastewater Effluents 

Figure 5 shows the HPLC-TEA chromatogram 
of a wastewater effluent sample obtained from a 
munition manufacturing facility. HMX is identi¬ 
fied in the sample, corresponding to 85 ng for a 5 
ul injection. The capability of the TEA analyzer 
interfaced to a gas chromatograph for another 
wastewater effluent analysis is demonstrated in 
Figure 6. In this sample, 2,4-DNT, TNT, and 
RDX were present (retention times 7.33, 8.76, and 
10.03 minutes, respectively). In addition, two 
other TEA peaks were observed at the retention 
time of 1.78 and 3.39 minutes. Given the matrix 
complexity of wastewater effluent where a number 
of other nitro-containing compounds may be pre¬ 
sent, the TEA technique could be used to selective¬ 
ly screen for all nitro compounds. 

A comparison study of the TEA analyzer with 
three other GC detectors: electrolytic conduc¬ 
tivity (HECD), thermionic (TSD) and electron 
capture (ECD), has been made for the analysis of 
nitroaromatics such as nitrobenzene, and isomers 


of dinitrotoluenes in sludge wastes by Phillips et 
al. (1983). The analysis of trace components in in¬ 
dustrial or municipal sludge is extremely difficult 
owing to matrix complexity. Figure 7 shows the 
chromatograms of the spiked sludge extract ob¬ 
tained using the ECD, HECD, TSD and TEA. 
The shaded areas correspond to the response of 
each detector for the spiked nitroaromatics—ni¬ 
trobenzene, 2,4-DNT, and 2,6-DNT—in the 
sludge extract produced by superimposing the 
standard response onto the individual chromato¬ 
grams. 

In the chromatograms obtained using the first 
three detectors, it was observed that a multitude of 
interfering peaks co-elute or elute at retention 
times close to the nitroaromatics, making accurate 
quantitation difficult. For the TEA, besides a 
broad “solvent peak’’, the only peaks observed 
were due to nitrobenzene, 2,4-DNT, and 
2,6-DNT. While all four detectors have inherent 
sensitivity towards standard nitro compounds, 
only the TEA analyzer can selectively detect the 
nitro compounds in the sludge samples. The use of 
the TEA analyzer does preclude the necessity for 
any further sample clean-up. 


CONCLUSION 

Analytical methods are developed for the trace 
analysis of various explosives and their nitrated 
metabolites in human plasma and wastewater ef¬ 
fluent. Monitoring and assessment of worker ex¬ 
posures to these compounds can now be routinely 
conducted through the use of the TEA analyzer. 

ACKNOWLEDGEMENT 

We thank Air Products for permission to repro¬ 
duce their chromatograms, shown in Figure 7. 


334 




DETECTOR RESPONSE (ARBITRARY UNITS) 


70 




0 4 8 



TIME 

(Minutes) 


TIME 

(Minutes) 


TIME 

(Minutes) 


A. RDX Standard, 
18 ng 


B. Plasma Blank 


C. RDX Spiked at 
5 ng/ml Level 


Figure 4. HPLC-TEA Analysis of RDX in Plasma. 


335 

















PETN 



L 

0 


8 


12 


16 


8 


TIME 

(Minutes) 


TIME 

(Minutes) 


Figure 5. HPLC-TEA Analysis of Wastewater Effluent A. Standard explosives B. Sample analysis. 


16 


336 


HMX 





















STANDARDS 


SAMPLE 



Figure 6. Capillary GC-TEA Analysis of Wastewater Effluent Standards—EGDN (2.84 min.), NG (5.94 min.), 2,4-DNT (7.35 
min.), TNT (8.72 min.), RDX (9.92 min.), Tetryl (11.32 min.). 


337 


10.03 





































I _I_I_I_I_I_I_ I _I_I_ I _I_1_I_ I _I_I 

024 6 8 10 12 14 16 

MINUTES 


ELECTRON CAPTURE 



i_i_i_i_i_i_i_i_i_i_l_i_i_l_l_l_l 

0 2 4 6 8 10 12 14 16 

MINUTES 


HALL ELECTROLYTIC 



MINUTES 



1 - 1 - 1 - 1 - 1 - 1 - 1 _ I _ I _ I _ I _ I _ I _ I _ I _ I _ I 

0 2 4 6 8 10 12 14 16 

MINUTES 


THERMIONIC 


TEA 


© Air Products and Chemicals, Inc. 1982 


Figure 7. Comparison of Four Selective GC Detector for Nitroaromatics. 


338 































































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340 


EXPLOSIVES AND GUNSHOT RESIDUE DETECTION 
BY APPLICATIONS OF ELECTROCHEMISTRY 


Robert C. Briner 

SEMO Regional Crime Laboratory 
Southeast Missouri State University 

Karl Bratin 

Bioanalytical Systems, Inc. 

C. Robert Longwell 
SEMO Regional Crime Laboratory 
Southeast Missouri State University 


ABSTRACT. Reductive and oxidative electrochemical detection with liquid 
chromatography is applied to the determination of nitro aromatics, nitrate esters, 
nitramines, and diphenylamines in military explosives and double base smokeless 
gunpowders. A sensitive and highly selective method is presented for the detection 
of organic “gunshot residue” on the hand of individuals who have discharged a 
weapon. The detection limits are of the order of 0.5, 1,2, and 0.3 picomol for nitro 
aromatic, nitramine and nitrate ester explosive compounds, and diphenylamines, 
respectively. In the last five years, oxidative mode electrochemical detection in 
liquid chromatography has become widely accepted for solving many problems of 
clinical, pharmaceutical, and environmental interest. Several reviews have been 
published on the advantages resulting from the combination of liquid chroma¬ 
tography with electrochemical detection (l.c.-e.c.). Progress in reductive mode 
(l.c.-e.c.) has been slow because of problems associated with dissolved oxygen, 
metal impurites, and the lack of reliable electrodes. Recent technological advances 
in detector design and the availability of more suitable electrode materials has gen¬ 
erated a renewed interest in this technique. This paper describes the application of 
reductive model (l.c.-e.c.) using glassy carbon and amalgamated gold electrodes to 
quantify explosive compounds in military explosives and smokeless gunpowders, 
and the development of a highly sensitive and selective method for the detection of 
nitroglycerin, 2,4-dinitrotoluene (2,4-DNT), and diphenylamine (DPA) in gun¬ 
shot residue. Most explosives can be classified into one of several groups repre¬ 
sented by nitro compounds, nitro acid esters, nitramines, salts of perchloric and 
chloric acids, azides and other miscellaneous compounds capable of producing an 
explosion, and mixtures of explosives from the above groups. Representatives of 
common commercial and military explosive compounds suitable for trace deter¬ 
minations using reductive mode l.c.-e.c. will be discussed. 


With the recent upsurge of terrorist and crimi¬ 
nal activity and the widespread use of firearms, 
law enforcement officials and forensic chemists 
have been interested in finding an effective and in¬ 
expensive method to determine whether an indi¬ 
vidual has recently fired a weapon. This informa¬ 
tion is valuable in investigations of alleged sui¬ 
cides, armed assaults, homicides and other activ¬ 
ities involving illegal use of firearms. In the 


process of criminal investigations it is also neces¬ 
sary to ascertain whether an individual has fired a 
weapon or handled a weapon which has been re¬ 
cently fired. 

As early as the 1930’s, law enforcement officials 
observed the presence of nitrates on the hands of 
individuals after they fired a weapon. The “paraf¬ 
fin cast” or “dermal nitrate” technique was de¬ 
veloped to measure residual nitrates. A paraffin 


341 


cast was formed on the suspect’s hands and after 
peeling it off, the inside of the cast was sprayed 
with diphenylamine reagent solution. The de¬ 
velopment of a blue color confirmed the presence 
of nitrate residue. Due to its simplicity, this 
method was quickly accepted and ruled admissible 
evidence in court proceedings, even though it has 
shown that more than thirty substances (including 
cigarette ash, urine, rust, and fertilizers) gave false 
positive results. 

As a result of numerous court challenges in the 
1950’s and 1960’s, the “paraffin cast’’ test was 
ruled inadmissible as evidence. Harrison and Gil¬ 
roy (1959) observed that metal components of bul¬ 
let and primer materials such as barium, lead, 
antimony and copper are deposited on the firing 
hand after discharging a firearm. Even though the 
Harrison-Gilroy colorimetric spot test was suit¬ 
able for laboratory determination of barium, anti¬ 
mony and lead, it was quickly found to be unsuit¬ 
able to reliably distinguish between the “hand 
blanks” and metal deposits formed after discharg¬ 
ing a weapon in actual firings. Nevertheless, the 
Harrison-Gilroy test demonstrated the need to 
quantitatively measure amounts of metals depos¬ 
ited on the hands. 

In the early 1960’s, neutron activation analysis 
(NAA) was shown to be suitable for trace determi¬ 
nation of metals in gunshot residue (GSR). Initial¬ 
ly, NAA was not widely accepted in forensic 
studies because only a few agencies were capable 
of performing time-consuming sample collection 
and processing. However, with the introduction of 
the cotton swab technique for sample collection 
(Hoffman, 1968; Goleb and Midkiff, 1974), NAA 
has become the leading method for the determina¬ 
tion of elevated levels of barium, antimony and 
copper in GSR. The high cost of instrumentation, 
the need for highly skilled personnel, the long 
analysis time, and the limited availability of NAA 
to local law enforcement agencies suggested 
flameless atomic absorption spectroscopy (FAAS) 
as a viable alternative method for the detection of 
metals in discharge residue (Krishnan, 1974; 
Kinard and Lundy, 1975; Stone and Petty, 1974). 
Other analytical methods which have been used to 
detect metals and particles in GSR include photo¬ 
luminescence (Jones and Nesbitt, 1975; Nesbitt, 
1977), flame emission spectroscopy (Stone and 
Petty, 1974), soft X-ray radiography (Stone and 
Petty, 1974), and X-ray fluorescence (Wood and 
Methiesen, 1974). Recently, several groups used 
scanning electron microscopy (SEM) to detect 


GSR particles (Andrasko and Maehly, 1977) and 
study the mechanism of GSR particle formation in 
order to distinguish them from their environ¬ 
mental sources of barium, lead and antimony. 

Forensic science and crime laboratories around 
the world are in constant need for improved 
methods for crime scene evidence analysis. Spe¬ 
cific and quantitative information is required by 
the investigator as rapidly as possible and since 
many determinations are not done on a routine 
daily basis, particularly in small, regional labs, the 
instrumentation should be inexpensive and easily 
maintained. To these ends, a method has been de¬ 
veloped for determining metallic residues on the 
hands of suspected felons using the technique of 
anodic stripping voltammetry (ASV). 

The ASV method has been shown to be a viable 
alternative to methods presently available such as 
common colorimetric tests ( e.g . the Dermal Ni¬ 
trate test and the Harrison-Gilroy color test) and 
the instrumental techniques of neutron activation 
analysis (NAA) and flameless atomic absorption 
(FAAS). ASV has been used for trace metal deter¬ 
mination in a large number of applications. In 
GSR analysis the metals of primary importance 
are copper, lead and antimony. Though copper 
and lead are commonly found in trace amounts on 
all individuals, the amounts found on hands that 
have recently fired a handgun increase significant¬ 
ly from base values. Antimony, on the other hand, 
even in trace amounts, is indicative of probable 
contact with a handgun. The ASV technique pro¬ 
vides simultaneous qualitative and quantitative in¬ 
formation for these elements (see Figure 1). 



Figure 1. Electrochemici Cell for Anodic Stripping Voltam¬ 
metry (ASV). 


342 














Some advantages of ASV are as follows: 

* microgram-per-liter sensitivity 

* freedom from optical interferences 

* compatibility with high ionic strength solu¬ 
tions 

* ability to determine valence states (speciea- 

tion) 

* capability for simultaneous multi-analyte 
determination (pattern recognition). 

In the ASV procedure, metals are preconcen¬ 
trated (reduced) from an electrolyte solution to a 
thin-film of mercury which has been deposited 
simultaneously on a carbon-based electrode 
(working electrode). The metals are then 
“stripped” (oxidized) from the mercury layer by 
changing the applied potential on the electrode. 
Since each metal has a characteristic potential at 
which it strips from the mercury layer and since 
the current required to remove the particular 
amount of metal from the mercury film is propor¬ 
tional to the original concentration, both qualita¬ 
tive and quantitative information can be obtained 
from a single experiment. The following proce¬ 
dure has been developed to apply the ASV tech¬ 
nique to practical use as an investigational aid for 
the determination of the trace metals copper, lead 
and antimony in gunshot residue analysis. 

RESIDUE SAMPLE COLLECTION 
PROCEDURE 

Residue sample collection requires: (5) cot¬ 
ton-tipped plastic handled swabs in plastic vials 
for storage and transportation; 5% nitric acid 
solution in a squeeze bottle; (2) pair plastic dispos¬ 
able gloves. 

Swab the appropriate area of the hands (right 
back, right palm, left back, left palm) with the 
cotton-tipped, plastic swabs that have been wetted 
with the 5% nitric acid solution. Note: The cotton 
swabs should not be touched without wearing the 
plastic gloves, and a new pair of plastic gloves 
should be used for each hand. Also make certain 
the plastic storage vials for the cotton swabs are 
appropriately labeled with the correct area of the 
hand swabbed and the control. 

GSR ANALYSIS PROCEDURE 

Reagents: 4M HC1 solution containing 0.02M 
hydrazine sulfate; 0.01 M HgCh. Equip¬ 
ment: CV-5 Bioanalytical Systems Voltammetry 
System. For this analysis, the initial potential on 
the CV-1B Controller should be set at - 1.0V, the 


anodic scan limit set to + 0.1V, the scan rate at 
20mV/s, the scan direction switch toggled to the 
-l- (anodic) position (this is a momentary contact 
switch), and the filter set to 1 s. See the CV-5 
manual for specific details on these adjustments. 
A GCE Glassy Carbon Working Electrode and 
RE-1 Silver/Silver Chloride Reference Electrode 
are used. Stirring is accomplished by a small mag¬ 
netic stirrer placed under the voltammetry cell and 
a small teflon stirring bar (ca. 1 cm length)(see 
Figure 1). A digital voltmeter in the system aids in 
verifying voltages of stripping peaks. 

Procedure 

1. Remove the plastic handles from the cotton 
swabs with scissors. 

2. Place the swab tip in a vial containing 4mL 
of the 4M HC1 with hydrazine solution 
(Note: There are five samples in each resi¬ 
due analysis, four from the suspect’s hands 
and one control). These samples are soaked 
for 1-3 hours, overnight if possible. 

3. Mix (vortex) and transfer contents of the 
vial to the electrochemical cell (see Figure 1) 
and add 100 L of the 0.01 M HgCl 2 solu¬ 
tion. 

4. Place the small magnetic stirring bar in the 
electrochemical cell containing the sample 
solution. 

5. Place the electrochemical cell in the cell 
compartment and insert the working and 
reference electrodes into the solution. 
Note: The glassy carbon working electrode 
should be polished and cleaned thoroughly 
before doing this analysis. Also check for 
air bubbles under the electrodes which can 
be removed by gently tapping the electrode 
body. Make certain the nitrogen tube is in 
place. 

6. Bubble nitrogen through the solution for 
180 seconds while stirring to purge dis¬ 
solved oxygen. 

7. Raise the nitrogen tube to just above the 
surface of the solution to provide an inner 
blanket of nitrogen during the actual analy¬ 
sis. 

8. Apply - 1.0V for 540 seconds with stirring 
followed by an additional 60 seconds with¬ 
out stirring. 

9. With the recording paper in place and pen 
down, scan positive at 20mV/s until the 
switching potential is reached ( + 0.1V) at 
which time the function switch is flipped to 


343 


the HOLD position and the working elec¬ 
trode is turned OFF. 

10. Clean the working electrode with deionized 
water and methanol following each run. 

A typical voltammogram from gunshot residue 
is shown in Figure 2. Note the characteristic 
stripping potentials of each of the metals. The 


amounts in each sample (Figure 2) are determined 
either by standard addition or by comparison with 
a calibration curve. Some typical test firing quan¬ 
titative data for antimony are shown in Table 1. 
These data have been correlated with data from 
flameless atomic absorption spectroscopy. 


Table 1. GUNSHOT RESIDUE DATA (TEST FIRING) FOR ANTIMONY (Sb) IN MICROGRAMS 4<g) [RB = Right Back; RP 

Sb( M g) 


= Right Palm; LB = Left Back; LP = Left Palm] 


Sample 

No. 

Gun & Bullet 

Condition 

1 

.38, 2" S&W 

before shot 


w/w Super 38 

after shot (outside) 


Special 

with right hand 

2 

.38, 2"S&W 

after shot washed 
hand then handled 
gun both hands 
before shot 


38 Special 

after shot with 

3 

.38, 2" S&W 

right hand 
before shot 

4 

.357,4", R&P 

after shot with 
right hand 

Indoor shot 

5 

.38, 2"S&W 

right hand 

Indoor shot 


R&P 

right hand 

6 

.38, 2/i ", S&W 

Indoor shot 


SW&P 

ND-not detected 


R-B 

R-P 

L-B 

L-P 

ND 

ND 

ND 

ND 

27 

15 

ND 

ND 


10 

66 

18.2 

92.8 

ND 

ND 

ND 

ND 

25 

32 

ND 

27 

ND 

ND 

ND 

ND 

35 

15 

12 

ND 

49 

340 

368 

440 

74 

65 

34 

280 

ND 

138 

ND 

ND 


Table 2. SUMMARY OF LC RESULTS ON A C 18 RE¬ 
VERSE PHASE COLUMN. 

Compound Detection Limits at S/N = 3 

UV (2.54) ECat-l.OV 


HMX 

1.5 ng 

0.29 ng 

Picric acid 

0.47 ng 

0.065 ng 

RDX 

0.88 ng 

0.17 ng 

Tetryl 

0.77 ng 

0.21 ng 

TNT 

0.65 ng 

0.14 ng 

Nitroglycerin 

160 ng 

0.38 ng 

2,4-DNT 

0.57 ng 

0.16 ng 

2,6-DNT 

1.2 ng 

0.17 ng 

3,4-DNT 

1.3 ng 

0.15 ng 

PETN 

— 

0.400 ng 


Typical concentrations of antimony in gunshot 
residue analysis following this procedure are 10 to 
40 ppb. Note that the linearity of the assay is lim¬ 
ited to approximately 100-120 ppb (See Figure 3). 
If concentrations are above this value, the sample 
should be diluted and re-run. Quantitation of 
antimony can be accomplished by standard addi¬ 
tion techniques or use of calibration curve. 


LCEC 

Reductive and oxidative electrochemical detec¬ 
tion with liquid chromatography can be applied to 
the determination of nitro aromatics, nitrate 

VOLTS 

0.0 - 0.5 -10 

1 I I-1-:-1 I_ '_I_i_ 'i 



Figure 2. Typical Voltammogram of Gunshot Residue. 


344 









Figure 3. Calibration Curve for Quantitation of Antimony 
(Sb) from Hand Swabs. 


esters, nitramines, and diphenylamines in military 
explosives and double base smokeless gun¬ 
powders. A sensitive and highly selective method 
is presented for the detection of organic (explo¬ 
sive) residue on individuals. The detection limits 
are of the order of 0.5,1,2, and 0.3 picomol for 
nitro aromatic, nitramine and nitrate ester explo¬ 
sive compounds, and diphenylamines, respective¬ 
ly- 

In the last five years, oxidative mode electro¬ 
chemical detection in liquid chromatography has 
become widely accepted for solving many prob¬ 
lems of clinical, pharmaceutical, and environ¬ 
mental interest. Several reviews have been pub¬ 
lished on the advantages resulting from the combi¬ 
nation of liquid chromatography with electro¬ 
chemical detection (LCEC). Progress in reductive 
mode (LCEC) has been slow because of problems 
associated with dissolved oxygen, metal impuri¬ 
ties, and the lack of reliable electrodes. Recent 
technological advances in detector design and the 
availability of more suitable electrode materials 
has generated a renewed interest in this technique. 

This paper describes the application of reduc¬ 
tive LCEC using glassy carbon and amalgamated 
gold electrodes (Au-Hg) to quantify explosive 
compounds in military explosives and smokeless 


gunpowders, and the development of a highly 
sensitive and selective method for the detection of 
nitroglycerin, 2,4-dinitrotoluene (2,4-DNT) by 
reductive mode, and diphenylamine (DPA) by 
oxidative mode. 

Chromatograms of common explosive mixtures 
such as nitroglycerin (Figure 4), COMP B (RDX 
and TNT), COMP C (RDX), C-4 (RDX), and 
Flex X (PETN) were investigated and typical 
chromatograms are shown in Figures 4 and 5. 

Table 2 shows a comparison of U.V. detection 
and electrochemical detection. The compound 
nitroglycerin which is present in most smokeless 
powders offers a possibility for detection of gun¬ 
shot residue on hand swabs as a comparison of 
nitroglycerin detector limits for U.V. vs LCEC 
(reductive) as LCEC is about 500X more sensitive 
than in U.V. detection. Preliminary work indi¬ 
cates nitroglycerin can be detected on hand swabs 
from test firing a handgun (.38 or .22). 


EXPERIMENTAL (LCEC) 

An LC-304T liquid chromatograph from Bio- 
analytical Systems equipped with an LC-300 solv¬ 
ent delivery system, Rheodyne 70-10 fixed volume 
(20 /uL) rotary sample injection valve, LC-22 


NITRO AROMATICS 



TNT LEAD STYPHNATE DIAZODINITRO 

PHENOL 


NITRATE ESTERS 


ch 2 ono 2 

CHONO, 

I i 

CH 2 0N02 


CHjONOj 

ch 2 ono 2 


CHjONOj 

o 2 noch 2 cch 2 ono 2 

CHjONOj 


NITROGLYCERIN EG DN 


PE TN 


NITRAMINES 



HMX 


RDX 


TETRYL 


Figure 4. Typical Explosives. 


345 









the HOLD position and the working elec¬ 
trode is turned OFF. 

10. Clean the working electrode with deionized 
water and methanol following each run. 

A typical voltammogram from gunshot residue 
is shown in Figure 2. Note the characteristic 
stripping potentials of each of the metals. The 


amounts in each sample (Figure 2) are determined 
either by standard addition or by comparison with 
a calibration curve. Some typical test firing quan¬ 
titative data for antimony are shown in Table 1. 
These data have been correlated with data from 
flameless atomic absorption spectroscopy. 


Table 1. GUNSHOT RESIDUE DATA (TEST FIRING) FOR ANTIMONY (Sb) IN MICROGRAMS (pg) IRB = Right Back; RP 
= Right Palm; LB = Left Back; LP = Left Palm] 


Sample 

No. 

Gun & Bullet 

Condition 

1 

.38, 2" S&W 

before shot 


w/w Super 38 

after shot (outside) 


Special 

with right hand 

2 

.38, 2"S&W 

after shot washed 
hand then handled 
gun both hands 
before shot 


38 Special 

after shot with 

3 

.38, 2"S&W 

right hand 
before shot 

4 

.357,4", R&P 

after shot with 
right hand 

Indoor shot 

5 

.38, 2"S&W 

right hand 

Indoor shot 


R&P 

right hand 

6 

.38, 2/i ", S&W 

Indoor shot 


SW&P 

ND-not detected 


Sb (Mg) 


R-B 

R-P 

L-B 

L-P 

ND 

ND 

ND 

ND 

27 

15 

ND 

ND 


10 

66 

18.2 

92.8 

ND 

ND 

ND 

ND 

25 

32 

ND 

27 

ND 

ND 

ND 

ND 

35 

15 

12 

ND 

49 

340 

368 

440 

74 

65 

34 

280 

ND 

138 

ND 

ND 


Table 2. SUMMARY OF LC RESULTS ON A C 18 RE¬ 
VERSE PHASE COLUMN. 

Compound Detection Limits at S/N = 3 

UV (2.54) ECat-l.OV 


HMX 

1.5 ng 

0.29 ng 

Picric acid 

0.47 ng 

0.065 ng 

RDX 

0.88 ng 

0.17 ng 

Tetryl 

0.77 ng 

0.21 ng 

TNT 

0.65 ng 

0.14 ng 

Nitroglycerin 

160 ng 

0.38 ng 

2,4-DNT 

0.57 ng 

0.16 ng 

2,6-DNT 

1.2 ng 

0.17 ng 

3,4-DNT 

1-3 ng 

0.15 ng 

PETN 

— 

0.400 ng 


Typical concentrations of antimony in gunshot 
residue analysis following this procedure are 10 to 
40 ppb. Note that the linearity of the assay is lim¬ 
ited to approximately 100-120 ppb (See Figure 3). 
If concentrations are above this value, the sample 
should be diluted and re-run. Quantitation of 
antimony can be accomplished by standard addi¬ 
tion techniques or use of calibration curve. 


LCEC 

Reductive and oxidative electrochemical detec¬ 
tion with liquid chromatography can be applied to 
the determination of nitro aromatics, nitrate 

VOLTS 

00 - 0.5 - 1.0 

-1-1-1-1-:-l, i-1— i i_i 



Figure 2. Typical Voltammogram of Gunshot Residue. 


344 










Figure 3. Calibration Curve for Quantitation of Antimony 
(Sb) from Hand Swabs. 


esters, nitramines, and diphenylamines in military 
explosives and double base smokeless gun¬ 
powders. A sensitive and highly selective method 
is presented for the detection of organic (explo¬ 
sive) residue on individuals. The detection limits 
are of the order of 0.5,1,2, and 0.3 picomol for 
nitro aromatic, nitramine and nitrate ester explo¬ 
sive compounds, and diphenylamines, respective¬ 
ly- 

In the last five years, oxidative mode electro¬ 
chemical detection in liquid chromatography has 
become widely accepted for solving many prob¬ 
lems of clinical, pharmaceutical, and environ¬ 
mental interest. Several reviews have been pub¬ 
lished on the advantages resulting from the combi¬ 
nation of liquid chromatography with electro¬ 
chemical detection (LCEC). Progress in reductive 
mode (LCEC) has been slow because of problems 
associated with dissolved oxygen, metal impuri¬ 
ties, and the lack of reliable electrodes. Recent 
technological advances in detector design and the 
availability of more suitable electrode materials 
has generated a renewed interest in this technique. 

This paper describes the application of reduc¬ 
tive LCEC using glassy carbon and amalgamated 
gold electrodes (Au-Hg) to quantify explosive 
compounds in military explosives and smokeless 


gunpowders, and the development of a highly 
sensitive and selective method for the detection of 
nitroglycerin, 2,4-dinitrotoluene (2,4-DNT) by 
reductive mode, and diphenylamine (DPA) by 
oxidative mode. 

Chromatograms of common explosive mixtures 
such as nitroglycerin (Figure 4), COMP B (RDX 
and TNT), COMP C (RDX), C-4 (RDX), and 
Flex X (PETN) were investigated and typical 
chromatograms are shown in Figures 4 and 5. 

Table 2 shows a comparison of U.V. detection 
and electrochemical detection. The compound 
nitroglycerin which is present in most smokeless 
powders offers a possibility for detection of gun¬ 
shot residue on hand swabs as a comparison of 
nitroglycerin detector limits for U.V. vs LCEC 
(reductive) as LCEC is about 500X more sensitive 
than in U.V. detection. Preliminary work indi¬ 
cates nitroglycerin can be detected on hand swabs 
from test firing a handgun (.38 or .22). 


EXPERIMENTAL (LCEC) 

An LC-304T liquid chromatograph from Bio- 
analytical Systems equipped with an LC-300 solv¬ 
ent delivery system, Rheodyne 70-10 fixed volume 
(20 /uL) rotary sample injection valve, LC-22 


NITRO AROMATICS 



TNT LEAD STYPHNATE DIAZODINITRO 

PHENOL 


NITRATE ESTERS 


ch 2 ono 2 

CHONO, 

I 1 

CH 2 0U02 


ch 2 ono 2 

CHjONOj 


ch 2 ono 2 

o 2 noch 2 cch 2 ono 2 

CHjONOj 


NITROGLYCERIN EGDN 


PETN 


NITRAMINES 



HMX 


RDX 


TETRYL 


Figure4. Typical Explosives. 


345 









RDX 



MINUTES MINUTES 


Figure 5. Mixture of Standard Explosives. 

temperature controller, LC-23A column heating 
compartment, the LC-4A electronic controller 
and the LC-19 accessories package were used in 
all LC determinations. The LC column was a Bio¬ 
phase ODS (25 cm). Spectrograde 1-propanol, 
triple distilled mercury, reagent grade anhydrous 
sodium acetate and monochloroacetic acid (all 
from Fisher Scientific) were used as purchased. 
All solvents for LC were filtered through 0.22 ptm 
Millipore filter (Millipore Corporation). Nitro¬ 
glycerine (NG) was obtained as a mixture in lac¬ 
tose (10% w/w) from Purdue University Phar¬ 
macy, West Lafayette, IN, and used without 
further purification. The mercury film electrode 
was prepared by placing enough triple distilled 
mercury on the highly polished gold surface to 
cover the entire surface. After 2-3 minutes, the ex¬ 
cess mercury was removed from the electrode sur¬ 
face using a computer card. MF-1 Microfilters 
with 0.2 fum regenerated cellulose filters (RC58) 
were used to filter GSR sample solutions. 

In summary, these procedures offer a unique 
approach to gunshot and explosive residue detec¬ 
tion of both trace organic and metals. A useful 


procedure is being developed to combine both of 
these analyses to the complex problem of GSR 
analysis in hopes of providing some useful data. 
The use of the dual electrode approach developed 
by Roston, 1982, should offer extended and more 
routine use of reductive LCEC as it eliminates 
many of the problems; mainly that of dissolved 
oxygen in both the mobile phase and the sample. 
A bibliography on both anodic stripping (ASV) 
and liquid chromatography with electrochemical 
detection (LCEC) is presented for informational 
use only. 

REFERENCES 

Andrasko, J. andMaehly, A. C. (1977). J. Foren¬ 
sic Sci. 22:279-87. 

Goleb, J. and Midkiff, C. (1974). Applied Spec¬ 
troscopy 28:768. 

Harrison, H. and Gilroy, R. (1959). J. Forensic 
Sci. 4:184. 

Hoffman, C. (1968). Identification News 18:7. 
Jones, P. F. and Nesbitt, R. S. (1975). J. Forensic 
Sci. 20:231-42. 

Kinard, W. D. and Lundy, D. R. (1975). ACS 
Symposium Series 12:97-107. 

Krishnan, S. S. (1974). J. Forensic Sci. 19:789-97. 
Nesbitt, R. S., Wessel, J. E., Wolten, G. M., and 
Jones, P. F. (1977). J. Forensic Sci. 
22: 288-303. 

Roston, D. A., Shoup, R. E., and Kissinger, 
P. T. (1982). Analytical Chemistry 54:1417A. 
Stone, I. C. and Petty, C. S. (1974). J. Forensic 
Sci. 19:784-8. 

Wood, W. G. and Mathiesen, J. M. (1974). Trace 
Element Analysis by Energy Dispersive X-Ray 
Spectroscopy. Finnigan Corp., Sunnyvale, Cali¬ 
fornia. 

ACKNOWLEDGEMENTS 

Dr. Karl Bratin, Purdue University, W. Lafay¬ 
ette, IN, now with Charles Pfizer Pharmaceuti¬ 
cal, Central Research, Groton, CT; Dr. Craig 
Bruntlett, Bioanalytical Systems, W. Lafayette, 
IN; Dr. Peter Kissinger, Dept, of Chemistry, Pur¬ 
due University, W. Lafayette, IN; Dr. Ronald 
Popham, Dept, of Chemistry, Southeast Mo. 
State University, Cape Girardeau, MO; Dr. Fred 
Sentfleber, Dept, of Chemistry, Murray State 
University, Murray, KY; Dr. Lowell Shank, Dept, 
of Chemistry, Western Ky. State University, 
Bowling Green, KY; Supaporn Chouchoiy, 
Graduate Student, Southeast Mo. State Univer¬ 
sity, Cape Girardeau, MO; Mike O’Connor, 


346 






















Graduate Student, Southeast Mo. State Univer¬ 
sity, Cape Girardeau, MO. 

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Shoup, R. E., et al., Ind. Research and Develop¬ 
ment 148, (May 1981). 

Weber, S. G., Anal Chem 54, 2126 (1982). Flow 
associated noise. 

Cyclicvoltammetry (CV) 

Heineman, W. R. and P. T. Kissinger, American 
Lab 29, (Nov 1982). CV. 


347 























EVALUATION OF FTIR AS A DETECTOR FOR THE HPLC 

ANALYSIS OF EXPLOSIVES 


Antonio A. Cantu, Willard D. Washington, 
Richard A. Strobel, and Richard E. Tontarski, 
Forensic Chemists, Forensic Science Branch, 
Bureau of Alcohol, Tobacco and Firearms, 
1401 Research Blvd., Rockville, MD 20850. 


ABSTRACT. HPLC has been used for some time, with a variety of detectors, for 
the identification of explosives. Unfortunately, the detector systems used with 
HPLC have lacked the necessary specificity for identification purposes. The ex¬ 
aminer must use alternate techniques to confirm his findings. In analyses involving 
actual cases the examiner is often confronted with chromatograms that provide 
him with multiple peaks having retention times close to those of known explosives. 
Being able to distinguish contaminants from explosives using only these retention 
times is inadequate for identification. If a sensitive and specific detector system 
could be applied to each component as it is eluted, the need for additional con¬ 
firmatory techniques could be eliminated. FTIR is such a detector. The use of 
HPLC coupled with FTIR as a detector is explored in this work, and it’s applicabil¬ 
ity to actual cases is evaluated. 


I. INTRODUCTION 

The analysis of explosive residue using high per¬ 
formance liquid chromatography (HPLC) with an 
ultraviolet (UV) detector offers high sensitivity, 
ie., nanogram amounts of explosives can be de¬ 
tected, but suffers in its specificity. Consequently, 
there is a need for a detector that has specificity 
and still retains the high sensitivity of the UV-de- 
tector. In this study the Fourier Transform Infra¬ 
red (FTIR) spectrometer is evaluated as such a de¬ 
tector. 

FTIR analysis differs from conventional infra¬ 
red (IR) analysis primarily in the speed of the 
analysis. Secondly, since many scans can be made 
within a short time period it is ideal for on-the-fly 
type of analyses such as the analysis of HPLC 
peaks. It can, also, offer higher sensitivity and 
resolution than conventional IR analysis. It 
should be noted that in general IR analysis pro¬ 
vides sensitivity for sub-microgram amounts of 
many compounds. 

In this study, the FTIR spectrometer coupled to 
a HPLC with a UV-detector was evaluated. The 
FTIR was used as a “confirmatory” or “more 
specific” detector of the eluting peaks. The FTIR 
can be used as an “on-line” or “off-line” detec¬ 


tor. In the latter case the HPLC fracton is collect¬ 
ed, stored, and concentrated prior to FTIR analy¬ 
sis. 

II. FTIR ANALYSIS OF BULK EXPLOSIVE 

The explosives considered were 2,4,6-trinitro¬ 
toluene (TNT), pentaerythritol tetranitrate 
(PETN), cyclotrimethylenetrinitramine (RDX), 
tetryl, and nitroglycerine. Potassium bromide 
micro-pellets were made of each explosive and the 
FTIR spectra obtained are shown in Figures I 
through 5. 

The FTIR system used was an Analect FX-6250 
instrument with the FXK-635 wideband HgCdTe 
detector assembly. 

III. HPLC ANALYSIS OF EXPLOSIVE 
MIXTURES 

The HPLC system used was a Waters Model 
6000 A Chromatographic Pump with a Model 441 
Absorbance Detector. It was set at 214 nm for de¬ 
tection. The mobile phase was a mixture of 70% 
acetonitrile and 30% water. The flow rate 1 
ml/min and the column was Waters C18 Radial 
Compression Module. Figures 6 and 7 show the 
HPLC separation of the explosives considered. 


349 


120. 0 j- 

i 

lio. o r 



FILE NAME 
#SCANS 
#BKC 
APOD 
COMMENT 


TNT IN KBr-3 MM DISC GAIN 

36 DET 

24 RES 

HANNING DATE 


1:49 CONC..BEAM CONDENSER 


4 ANALECT FX-6250 

ORD : 7.1 

4 CM-1 ABSC: WAVENUMBER 

1/ 25/83 


Figure 1. FTIR Spectra of TNT in KBr. 


IV. THE COUPLING OF THE FTIR TO 
THE HPLC 

The key device in the coupling of the HPLC 
with the FTIR is a flowthru cell with a beam con¬ 
denser. The beam condenser is a Barnes Model 
600 which claims to give a 16-fold increase in en¬ 
ergy density. The flow-thru cell used is a Barnes 
demountable micro-flow-thru cell. This versatile 
cell can be assembled to give various pathlengths 
and corresponding cell volumes. The flow-thru 
cell is shown in Figure 8. 

V. DETERMINATION OF THE OPTIMUM 
PATHLENGTH IN THE FLOW-THRU CELL. 

First, we examined the FTIR spectra of TNT, 
PETN, RDX and tetryl explosives in the acetoni¬ 
trile-water mobile phase. This being an aqueous 
system requires the use of cell windows insoluble 
in water. Cells of this nature are KRS-5 and 
Itran-2. We selected the KRS-5, because of its 
wider transmission range. The FTIR spectra of the 
explosives in this aqueous system were made using 


the demountable flow-thru cell with beam con¬ 
denser. The cell separation or pathlength chosen 
was 0.1 mm. This analysis did not require coup¬ 
ling to the HPLC. Figure 9 shows the FTIR spec¬ 
trum of the aqueous system, i.e., the HPLC mo¬ 
bile phase of 70% acetonitrile and 30% water. In 
comparing these spectra to the pure explosives 
(Figure 1 to 5) one can see that there is consider¬ 
able masking of many explosive peaks. Figures 10 
to 13 show the spectra for TNT, RDX, PETN and 
tetryl, respectively. Each has the solvents removed 
as background, so theoretically, the resultant 
spectra are due mainly to the explosive. It should 
be noted that these spectra have a vertical scale ex¬ 
pansion. The concentration of each explosive is 
1000 ppm. The shaded peaks correspond to the ex¬ 
plosive peaks that remain after the subtraction of 
solvent from explosive plus solvent. 

Next the optimum pathlength had to be deter¬ 
mined. Here TNT was chosen for this determina¬ 
tion. Figure 14 gives the pathlengths available in 
the flow-thru cell and the corresponding cell vol¬ 
umes. The aperture used was the standard 3 mm. 


350 
















































120. D r 



FILE NAME : PETN IN KBr-3MM GAIN 

#SCANS : 36 DET 

#BXG : 24 RES 

APOD : HANNING DATE 


COMMENT : 1:49 CONC..BEAM CONDENSER 


2 SORT (2) ANALECT FX-6250 
ORD : %T 

4 CM-1 ABSC: WAVENUMBER 
1/ 25/83 


Figure 2. FTIR Spectra of PETN in KBr. 


The concentrations considered for TNT were 
1000 ppm, 500 ppm, 250 ppm and 125 ppm. Fig¬ 
ure 15 gives the minimum amount (in nanograms) 
that was detected with each pathlength consid¬ 
ered. The double line between the amounts detect¬ 
ed for concentrations of 250 ppm and 125 ppm in¬ 
dicate that a concentration of 250 ppm is easily de¬ 
tected but not the concentration at 125 ppm. The 
interesting thing observed here is that as the cells’ 
pathlength diminish and thus becomes more trans¬ 
parent to the HPLC mobile phase the minimal 
concentration detected does not increase as antici¬ 
pated but remains the same. Therefore, the trans¬ 
parency of the mobile phase is increasing more 
rapidly than the decrease in concentration of sam¬ 
ple due to the shortening of the cell pathlength. 

VI. HPLC PEAK VOLUME vs MICRO-CELL 
VOLUME 

From the conclusions reached by the optimum 
pathlength determination a pathlength between 
0.015 mm to 0.1 mm permits 250 ppm to be detect¬ 
ed. The absolute amounts detected are calculated 


using the corresponding cell volumes. The 
amounts are between 32.5 and 250 ng for a con¬ 
centration of 250 ppm. 

The remaining question is what minimal quanti¬ 
ty of explosive must be present in the eluant peak 
delivered by the HPLC to the FTIR in order for 
the FTIR to detect it. The answer is not very en¬ 
couraging. In Figure 16 an equation is developed 
for relating the weights of explosives in the HPLC 
peak volume and in the micro-cell. It is based on 
the simplified model of the peak volume being 
uniform in concentration. 

Considering an average peak volume of 300 ul, 
the amount needed from the HPLC at a concen¬ 
tration of 250 ppm is 75 ug. (Figure 17). Clearly, 
this is not as sensitive as the UV-detector but does 
offer more specificity. 

CONCLUSION 

This work has focused on optimizing the 
flow-cell pathlength in order to detect an explo¬ 
sive peak in the HPLC mobile phase. The second 
phase was to establish lower limits of detection for 


351 



































120 . 0 


1 

I 

1 10. 0 t 


100 . 0 ‘ 



FILE NAME 

#SCANS 

#BKG 

APOD 

COMMENT 


TETRYL IN KBr-3MM CAIN 

36 DET 

24 RES 

HANNING DATE 


1:49 CONC..BEAM CONDENSER 


4 ANALECT FX-6250 

ORD : %T 

4 CM-1 ABSC: WAVENUMBER 

1/ 26/83 


Figure 3. FTIR Spectra of Tetryl in KBr. 


the explosive within the cell. After optimizing the 
flow-cell size in order to detect the explosive it be¬ 
came apparent that the concentration of explosive 
in the HPLC eluant would not be sufficient for de¬ 
tection. In order to overcome this a larger (longer 
pathlength) volume cell would have to be used. 
But as was seen in the experiment an increase in 
cell size produced an increase in the HPLC mobile 
phase which made the cell less transparent. 

The method does not allow for a small quantity 
of material (explosives) to be identified in a large 
amount of IR absorbing solvent. The fine details 
of the IR spectra necessary for compound identifi¬ 
cation are obscured. Only the major bands of the 


explosives can be seen. While not providing suffi¬ 
cient information for positive identification they 
do provide additional information to that provid¬ 
ed by the UV-detector. The method at this point 
does not lend itself to on-the-fly analysis. A fu¬ 
ture possibility, when using this type cell would be 
to find a more IR transparent HPLC solvent sys¬ 
tem. 

ACKNOWLEDGEMENT 

The authors thank Miss Lisa Wellington, an in¬ 
tern from the Forensic Science Undergraduate 
Program at the University of Central Florida, Or¬ 
lando, FL, for assisting us in this project. 


352 





















































120. 0 j- 

110 . 0 * 


100 . 0 ■ 



FILE NAME 

#SCANS 

#BKG 

APOD 

COMMENT 


NG XT: ACETONE GAIN 

36 DET 

24 RES 

HANNING DATE 


3MM DISC.3 TABS (START) 


4 

4 CM-1 


ANALECT FX-6250 
ORD : %T 

ABSC: WAVENUMBER 


Figure 4. FTIR Spectra of Nitroglycerine in acetone. 


353 









120.0 f 


110.0 * 

100 . 0 * 

90. 00 - 

BO. 00 * 

70. 00 * 

60. 00 • 

50. 00 

40. 00 

30. 00 

20. 00 

10 . 00 

0 . 000 

4 400 



FILE NAME : 
#SCANS : 
#BKG : 
APOD : 
COMMENT : 


RDX IN KBr-3 MM DISC CAIN 

36 DET 

24 RES 

HANNING DATE 


1:49 CONC. . BEAM CONDENSER 


4 

4 CM-1 
1/ 25/83 


ANALECT FX-6250 
ORD : %T 

ABSC: WAVENUMBER 


Figure 5. FTIR Spectra of RDX in KBr. 




































. ■} . 4 .• L N 

-j , i H l_! f S 
02. *0. 13.4h. 


f'1 P L H 
I'tpT 4 

•it THOD 


. ► i 


4 i 



4 

NHM£ lOE 

■- JNC 

•1V 

4R£H 

4 

.. 34 

.Ob 9 


3014 

.1 

.. T*y 

4 092 

/ 

41 39 

4 

3. I j 

3.4 85 


.312 

Vi 

3.43 

4 . -:0 b 

1 

• • 

■473b 

0 

S’ J 

-• • 

J. 3 * 3 

\l 

1173 

.0 

4.21 

20.0209 

1 1 

4 8 3 3 

0 

4.4 1 

3..44l 

« t • 

2538 

0 

4.53 

i'4. 0354 

- t 1 

4398 

0 

3.04 

’.4521 


38 73 


rriTHL 

49.4999 


4 9 3 8 3 


Figure 6. HPLC separation of HMX, RDX, Tetryl, TNT and PETN. 


355 


































Ui iiJ 


: j - • i ■ j n i ' -* n [:* h R L-' 

•j >i sj R C> r*l i v_i IjL l , -.1 RuF S 





♦ 

* * 

o 

Ol 


, - t i h 

MPf_ 4 .1 ij 

L 4 

■ t * ■ ; d t 

H f I j > 4 1 


4 

'-.I 

ij 

•J 

il 




4 

TOTftL 


ME 

4 

vi 4 

44 

45 


. ‘J Nl_ 

1 . ~ r. 

- "r . J :• 

4. -:5~f 

-*, ‘i4Sy 

5 . 28*4 

-(■4 4 ’4m 4 


] 



4RER 
r 01 .3 4 
1724 
i 8 1 40 
1U534 
201083 



Figure 7. HPLC separation of NG, EGDN. 


356 


EGDN 





















Micro Flo-Thru Cell 



KRS-5 


tr^EX/T TUBING 


MODIFIED 

SWAGELOK 

FITTING 

O-RING 


IR WINDOW 


SPLIT 

SPACER u. . 




y BODY 


1/16 TUBING 
USER SPECIFIED I.D. 


Figure 8. Barnes Micro Flo-Thru cell. 


357 






























I 1 * I » 1 

2000 1800 1800 


* * i * i. - 

MOO 1200 1000 


800 


i. .!_( 

800 400 


FILE NAME : 
#SCANS s 
#BKG s 
APOD : 
COMMENT : 


SOLV = CH3CN + H20 GAIN 

32 DET 

32 RES 

TRAPEZOIDAL DATE 


BKGND=EMTY CELL PL=.015MM 


4 SORT(2) ANALECT FX-6250 
ORD c %T 

4 CM-1 ABSC: WAVENUMBER 


Figure 9. FT1R Spectra of the HPLC mobile phase; 70% Acetonitrile and 30% HOH. 


358 



































105. 0 


104. 2 

103. 5 

102. 7 

102. 0 

101 . 2 

100. 5 

99. 75 


99. 00 


98. 25 

97. 50 

90. 75 


J 

4400 4000 

3800 3200 

2800 2400 2000 

1800 1000 

1400 1200 

1000 

800 000 400 

1 FILE NAME 

1 

SOLVENT 

+ TNT 

GAIN 

i 

4 

ANALECT FX-6250 

#SCANS 

1 

64 


DET 

i 


ORD . 

XI 

#BKG 

1 

64 


RES 

i 

4 CM-1 

ABSCi 

WAVENUMBER 

APOD 

1 

HANNING 


DATE 

> 




COMMENT 

t 

BKGND = 

SOLVENT 








Figure 10. FTIR Spectra for TNT after subtraction of HPLC mobile phase spectra. 


359 



























103.5 * 


102. 7 

102. 0 

101. 2 

100. 5 

99. 75 

99. 00 

98. 25 

97. 50 

98. 75 



i 

96.00 1 -*- •—* » - 1 * 

4400 4000 3800 3200 2800 2400 2000 


-1 4 - -4- 4- 4-- *-• .1.- 4- l_ A 1-4 - 1 - 

1800 1000 1400 1200 1000 800 000 



! FILE NAME . SOLVENT + RDX 
#SCANS . 64 

1 #BKG . 64 

iAPOD . HANNING 

|COMMENT . BKGND = SOLVENT 


GAIN .4 
DET . 

RES « 4 CM-1 
DATE . 


ANALECT FX-6250 
ORD « XT 

ABSC. WAVENUMBER 


Figure 11. FTIR Spectra for RDX after subtraction of the HPLC mobile phase spectra. 


360 





















105. 0 


104.2 f 


103.5 * 


102. 7 ♦ 


102. 0 


101.2 ' 


100. 5 


99. 75 


99. 00 


98. 25 ► 


97. 50 1 


96. 75 


96. 00 



4 400 


4000 3600 


3200 2800 2400 2000 1800 1600 1400 


_i_.__—i—- 

1200 1000 


800 600 400 


FILE NAME 

i 

SOLVENT - PETN 

GAIN 

s 4 

ANALECT FX-6250 

#SCANS 

i 

64 

DET 

t 

ORD t %T t 

! #BKG 

t 

64 

RES 

« 4 CM-1 

ABSC. WAVENUMBER | 

i APOD 

t 

HANNING 

DATE 

i 

} 

,COMMENT 

L - . 

> 

BKGND = SOLVENT 



1 

i 


Figure 12. FT1R Spectra for PETN after subtraction of the HPLC mobile phase spectra. 


361 






























105.0 


104.2 

103. 5 


102. 7 


102.0 


101.2 f 


lOO. 5 


99. 75 


99.00 (• 


96. 25 


97. 50 


90. 75 


90. 00 



D --- * -*— 

4400 4000 

-1-4,--4- 

3000 3200 

-i~ — .a -1-* 

2800 2400 

2000 1800 1600 

-1--4- . i- 

1400 1200 

-i--*— 

lOOO 

900 600 400 

FILE NAME 

1 

SOLVENT 

+ TETRYL 

GAIN « 

4 

ANALECT FX-6250 

#SCANS 

1 

64 


DET . 


ORD . 

%T 

#BKG 

1 

64 


RES . 

4 CM- 1 

ABSCi 

WAVENUMBER 

APOD 

1 

HANNING 


DATE . 




COMMENT 

I 

BKGND = 

SOLVENT 




1 


Figure 13. FTIR Spectra for Tetryl after subtraction of the HPLC mobile phase spectra. 


362 






































OPTIMUM PATHLENGTH 


HPLC PEAK VOLUME -vs- MICRO CELL VOLUME 


B PATHLENGTHS (CELL VOLUMES) CONSIDERED 


Pathlength (mm) 

.015 

.025 

.05 

.10 

.20 

.50 

1.0 

Volume (pi) 

.15 

.26 

.51 

1.0 

2.0 

5.1 

10.1 


3mm Aperture for standard Spacers 


V - Peak Volume 

A - Weight of Explosive 
in Peak Volume 



A - a(V/v) 


v - Cell Volume 

a - Weight of Explosive 
in Cell 


Figure 14. Available pathlengths and cell volumes considered. Figure 16. Development of an equation relating explosive 

weight in a given HPLC peak volume to cell volume and weight 
in the cell. 


OPTIMUM PATHLENGTH 

D. MINIMUM AMOUNT (IN ng) DETECTED 
PER EACH PATHLENGTH 


Pathlength (mm) 

.015 

.025 

.05 

.10 

.20 

.50 

1.0 

Volume (pi) 

.15 

.26 

.51 

1.0 

2.0 

5.1 

10.1 

Cone. 

1000 ppm 

150 

260 

510 

1000 


500 ppm 

75 

130 

255 

500 

250 ppm 

37.5 

65.0 

128 

250 

125 ppm 

18.8 

32.5 

63.8 

125 


Figure 15. Optimum pathlength. Minimum amount (in ng) de¬ 
tected per each pathlength. 


HPLC PEAK VOLUME -vs- MICRO CELL VOLUME 
. . . CONTINUED 

AVERAGE PEAK VOLUME V =300 pi 


Pathlength (mm) 

.015 

.025 

.05 

.10 


v - Volume (pi) 

.15 

.26 

.51 

1.0 

A 


1000 ppm 

150 

260 

510 

1000 

300 pg 

O 

c 

500 ppm 

75 

130 

255 

500 

150 pg 

o 

O 

250 ppm 

37.5 

65.0 

128 

250 

75.0 pg 


125 ppm 

18.8 

32.5 

63.8 

125 

37.5 pg 


a(ng) 


Figure 17. Table relating cell pathlength, cell volume and ex¬ 
plosive concentration. 


363 














































































































































































































MISCELLANEOUS METHODS 



















































FORENSIC COMPARISON OF EXPLOSIVE SAMPLES BY PROTON MAGNETIC 

RESONANCE SPECTROMETRY 


Hans-Dieter Schiele + 
Gottfried Vordermaier + + 
Bundeskriminalamt 
D 6200 Wiesbaden 
Federal Republic of Germany 


ABSTRACT. Qualitative and quantitative determination of significant by-prod¬ 
ucts and trace impurities is useful as additional forensic information to differenti¬ 
ate between materially equal explosive compounds originating from different 
sources. For this purpose chromatographic techniques (especially HPLC) and nu¬ 
clear magnetic resonance are used. An example of the application of NMR-spec- 
trometry for the rapid and simple characterization of organic explosives is demon¬ 
strated. The detection of low levels of a specific impurity (trinitroanisole) in tri- 
nitroaniline samples allows comparative analysis and also the establishment of 
relevant connections. Furthermore, the NMR-analytical identification of this 
characteristic explosive impurity furnishes indications concerning the manufactur¬ 
ing process. 


The analysis of explosives and of their residues 
after explosions carried out by means of a wide va¬ 
riety of chemical and physical examination meth¬ 
ods has been repeatedly studied and was subject of 
many scientific publications. Moreover, it is above 
all the determination of small quantities of addi¬ 
tives or impurities that frequently leads to a differ¬ 
entiation of homogenous explosives of different 
origin. Such distinctive features may be condi¬ 
tioned by different manufacturing processes, ad¬ 
mixtures of additives, the utilization of starting 
material of varying quality, but also by variations 
between the individual charges as well as aging or 
climate influences (heat, moisture) and other fac¬ 
tors. This additional analytical information 
concealed in the sample often facilitates a better 
specification of the proof by forensic science and, 
thus, enables the forensic comparison of samples 
or even existing leads to links between crime cases. 

A successful analysis of such significant addi¬ 
tives or impurities or the “fingerprinting” of ex¬ 
plosives is achieved on the one hand by means of 
various chromatographic techniques, especially by 
High Pressure Liquid Chromatography (HPLC) 
[Krull and Camp, 1980] and on the other hand 

+ Dr. Ing., Chemist, Forensic Science Laboratory 
+ + Dr. rer. nat., Chemist, Forensic Science Laboratory 


above all by means of Nuclear Magnetic Res¬ 
onance Spectrometry (NMR) [Schiele and Vorder¬ 
maier, 1982]. 

The presence of impurities, additives, etc. in a 
substance to be examined may be recognized in the 
NMR spectrum by the occurrence of additional 
resonance signals or—in case of superposition— 
by non stoichiometric proportions in the integra¬ 
tion. The signal areas are proportional to the rela¬ 
tive number of the related hydrogen atoms and, 
thus, reflect the extent of impurity involved, 
whereas chemical shifts, multiplet structures and 
intensities allow to draw conclusions as to the kind 
of impurity given in the individual case. Thus, 
NMR spectrometry renders possible the simple 
and quick simultaneous presentation of specific 
impurity patterns as well as mixtures of organic 
explosives constituents. Let us illustrate this by a 
practical example: 

Recently, an about 80-year-old pensioner was 
suspected, in spite of his old age, to occasionally 
supply against payment anarchist circles with ex¬ 
plosives. When his weekend house was searched, 
chemicals were found as well as detonators, wires 
and tools of older design which are appropriate 
for the manufacture of explosive devices (Figure 
1). Furthermore, traces were found and preserved 


367 


Figure 1. Seized chemicals and tools used to manufacture explosive devices. 



in the surroundings of the secluded house which 
raised the suspicion that presumably test explo¬ 
sions had been made there a short time before. 

During forensic examination of the exhibits the 
interest was soon concentrating on a yellow sub¬ 
stance similar to picric acid which had been seized 
in powdered form, but also in pressed bars and 
partly mixed with potassium nitrate and other in¬ 
organic substances. By 1R- and 1 H- NMR spectro- 
metric methods it was possible to quickly identify 
this chemical as 1 - amino-2,4,6-trinitro-benzene 
(trinitroaniline, TNA, picramide). Trinitroaniline 
which is produced by reaction of trinitrochloro- 
benzene with ammonia or nitrating of nitraniline 
has found but little application as an explosive in 
former times, however, was used during World 
War II to a limited extent and mostly mixed with 
TNT. Nowadays, it seems that it has almost no 
significance anymore as an explosive. 


In the proton magnetic resonance spectrum of 
trinitroaniline (Figure 2b) appears the intensive 
clear-cut singlet of two protons at the six-mem- 
bered ring in the expected region of trinitro-sub- 
stituted aromatic compounds and is superimposed 
by a broad, strong down field shifted signal of the 
amino group. In the sample spectrum (Figure 2a) 
two additional small signals at 9.08 and 4.18 ppm 
appear which, according to 'H-NMR analysis are 
to be allocated to the chemical substance 2,4,6—tri- 
nitroanisole (Figure 2c). From the relation of the 
integrated signal area the portion of this additive 
to approximately 2.5 mol% may be calculated. It 
is characteristic that these impurity signals-in 
comparable percentage-are detected in all 
TNA-containing exhibits pertaining to the crime 
case concerned, also in the cut samples. 

The provenance of the slight share of trinitro- 
anisole (on account of its sensitiveness to hydroly- 


368 





“I I-1--—I--- T..1-1-!-1-1-1- 

10 98765432 10 PP m 



10 98765432 1 0 ppm 

_i_1_i_i-1-1-i-1-1-i-1- 


Figure 2. Proton NMR spectra 


369 

























sis and its toxicity virtually meaningless as an ex¬ 
plosive agent) seems at first sight unclear. How¬ 
ever, comprehensive literature research furnished 
indications that—differing from the usual, above- 
described manufacturing process—trinitroaniline 
was in former times partly also prepared out of tri- 
nitroanisole (Figure 3). This would imply that this 
specific “marker” results from the manufacturing 
process and can be attributed to chemically un¬ 
changed starting material. 



trinitroanisole 


+ NH, 

-—► 

-CHjOH 



Figure 3. Former synthesis of trinitroaniline via trinitroani¬ 
sole. 


In our above-mentioned example a date of 
manufacture can be deduced from the results of 
the analysis of the examined TNA-sample that lies 
in a rather remote past. This fact corresponds to 
the old age of the suspect and the rest of the seized 
evidence. 


Spectrometer: 

system: 

Data System: 


Fourier NMR- 
Spectrometer 
BRUKER WH90 
ASPECT 2000 
Computer with 
High Density 
Floppy Disk System 


NMR-Solvent: Acetone—d 6 

Standard Tetramethylsilane 

(int.): (TMS) 

SUMMARY 

Qualitative and quantitative determination of 
significant by-products and trace impurities is 
useful as additional forensic information to differ¬ 
entiate between materially equal explosive com¬ 
pounds originating from different sources. For 
this purpose chromatographic techniques (espe¬ 
cially HPLC) and Nuclear Magnetic Resonance 
are used. 

An example of the application of NMR-spec- 
trometry for the rapid and simple characterization 
of organic explosives is demonstrated. The detec¬ 
tion of low levels of a specific impurity (trinitro¬ 
anisole) in trinitroaniline samples allows compara¬ 
tive analysis and also the establishment of relevant 
connections. Furthermore, the NMR-analytical 
identification of this characteristic explosive im¬ 
purity furnishes indications concerning the manu¬ 
facturing process. 

REFERENCES 

Krull, I. S. and Camp, M. J. (1980). Analysis of 
explosives by HPLC. American Lab. 
12: 63-76. 

Schiele, H.-D. and Vordermaier, G. (1982). For- 
ensische Charakterisierung von Explosivstoffen 
durch NMR-Analytik spezifischer “Verun- 
reinigungs”-Muster am Beispiel von Trinitro- 
anilin. Arch. Kriminol. 169: 155-160; Chem. 
Abstr. 97 (1982) Nr. 200312 t. 


370 









RADIOFREQUENCY RESONANCE ABSORPTION SPECTROSCOPIC (RRAS) 
METHODS FOR THE DETECTION AND ANALYSIS OF EXPLOSIVES 


William L. Rollwitz 
J. Derwin King 
Southwest Research Institute 
6220 Culebra Road 
Postal Drawer 28510 
San Antonio, Texas 78284 


ABSTRACT. The field of radiofrequency resonance absorption spectorscopy 
(RRAS) comprises the techniques of nuclear magnetic resonance (NMR), nuclear 
quadrupole resonance (NQR), and electron magnetic resonance (EMR), all of 
which are useful in the detection and qualitative and quantitative analysis of explo¬ 
sives. Each of these techniques can be used on some but not all explosives. Hydro¬ 
gen NMR signals can be obtained with good signal-to-noise ratio from all explo¬ 
sives except black powder. Nitrogen NMR signals are also available from many ex¬ 
plosives. Nitrogen NQR spectra can be obtained from a few explosives. Free elec¬ 
tron EMR responses are available from those explosives containing pyrolyzed ma¬ 
terials. Each of these techniques will be briefly described, their expectations com¬ 
pared, and some results, from many years of measurement experience, displayed. 


I. BACKGROUND 

Southwest Research Institute has been making 
nuclear magnetic resonance measurements on 
explosives and propellants since 1956, and de¬ 
veloping specialized magnetic resonance equip¬ 
ments for performing specific measurements on 
propellants and explosives since 1958. From 1958 
to 1960, two equipments were developed for 
Thiokol Corporation to measure the concentra¬ 
tions of aluminum and hydrogen in a solid propel¬ 
lant mixture just before it is poured in the casing. 
From 1964 to 1970, a moisture meter for black 
powder and M-10 propellant was constructed for 
Picatinny Arsenal. From 1968 through 1970, a 
magnetic resonance device was made to measure 
the amounts of water and nitric acid in the 
three-part mixed acid of a nitrating plant produc¬ 
ing TNT and nitrocellulose’. By subtraction, the 
amount of sulfuric acid was determined. From 
1973 through 1977, a magnetic resonance device 
was constructed to detect explosives hidden in the 
ground. From 1976 to the present, magnetic 
resonance devices have been constructed to detect 
explosives hidden in letters, baggage and large 
containers. During these equipment develop¬ 
ments, nuclear magnetic resonance measurements 


have been made on many types of explosives and 
propellants, and many other applications for 
qualitative and quantitative analyses have been in¬ 
dicated. Some of these application possibilities 
will be described in the next section, followed by a 
brief description of the magnetic resonance phe¬ 
nomena and a discussion of the information which 
can be obtained from the magnetic resonance sig¬ 
nals from some explosives and propellants. The 
last section will give brief descriptions of some of 
the instrument manifestations which are possible. 

II. NMR APPLICATIONS TO EXPLOSIVES 
AND PROPELLANTS 

Many NMR measurements have already been 
performed at SwRI on explosives and propellants. 
These will be discussed in Section IV. The data 
from these measurements have led to the follow¬ 
ing conclusions: 

(a) The hydrogen NMR signals from solid ex¬ 
plosives have very short values of T 2 (7 to 50 
microseconds) and very long values of Ti (3 to 300 
seconds at 3.0 MHz). 

(b) Solid explosives such as RDX and TNT 
have strong spin-spin coupling between the hydro- 


371 


gen and nitrogen nuclei when the hydrogen NMR 
resonating frequency is made equal to the nitro¬ 
gen-14 nuclear quadrupole resonance frequency. 

(c) The hydrogen NMR signals from the liquid 
components of explosives and propellants in¬ 
cluding moisture, have longer values of T 2 (1 to 
200 milliseconds) and much shorter values of Ti (1 
to 200 milliseconds) than do the solid components. 

(d) Useful signal/noise ratios are obtained for 
the hydrogen transient NMR signals from the high 
concentration components of the solid explosives 
and propellants with magnetic fields of from 500 
to 1000 Gauss. 

(e) Useful signal/noise ratios for low concen¬ 
tration liquid materials such as moisture with 
longer values of T 2 may require a higher magnetic 
field for an accurate measurement, perhaps as 
high as 7000 Gauss, or a hydrogen resonance fre¬ 
quency of around 30 MHz, for concentrations of 
from 0.1 to 1 percent. 

(0 The charcoal used in black powder and as a 
coating on some propellants gives a strong free 
electron magnetic resonance signal. 

The above conclusions have indicated several 
measurement possibilities using hydrogen tran¬ 
sient NMR signals. Among these possibilities are: 

(a) Constituent quantitative analyses can be 
made in explosives and propellants in their solid 
form. The types considered have been: Composi¬ 
tion B, Composition A, Composition C, deto¬ 
nator mixtures such as M-55, and RDX (HMX 
concentrations). 

(b) Solid/liquid ratios in flowing slurries of ma¬ 
terials such as TNT and Composition B as well as 
the RDX and TNT concentrations can be deter¬ 
mined. 

(c) Moisture measurements can be made in 
fixed samples and flowing streams up to one inch 
I.D. for all explosives and propellants. 

(d) The hydrogen NMR signal from the incom¬ 
pletely pyrolyzed hydrocarbon material in char¬ 
coal can be used as a quality control to measure 
the amount of pyrolyzation. 

(e) The hydrogen NMR signal from the in¬ 
completely pyrolyzed hydrocarbon material and 
from the moisture can be used to give a 
non-weighing determination of the moisture in 
black powder and in the charcoal as a raw mate¬ 
rial. 

(0 The free electron magnetic resonance signal 
from charcoal can also be used as a quality control 
measurement on it as a raw material. 

(g) The free electron signal can be used in com¬ 


bination with the hydrogen NMR signal from the 
water to make a non-weighing measurement of 
percent moisture in black powder if there is no hy¬ 
drogen signal from the incompletely pyrolyzed hy¬ 
drocarbon in the charcoal. 

III. THE PHENOMENA OF MAGNETIC 
RESONANCE 

Magnetic resonance is a type of absorption 
spectroscopy involving the resonance absorption 
of electromagnetic energy caused by the interac¬ 
tion of the magnetic moments of nuclei or free 
electrons with a magnetic bias field. Not all nuclei 
and electrons have magnetic moment. Nuclei have 
a magnetic moment when they have even-odd or 
odd-even combinations of protons and electrons. 
Thus, hydrogen-1, oxygen-17 and carbon-13 nu¬ 
clei have magnetic moment; oxygen-16 and car¬ 
bon-14 nuclei do not. Electrons have a magnetic 
moment only when they are single and free. Pairs 
of electrons, in orbit for example, pair by the 
Pauli pairing principle to produce no net magnetic 
moment. 

Without the magnetic bias field, there are no 
resonant absorption frequencies. When nuclei and 
electrons with a magnetic moment are placed in a 
bias magnetic field, the nuclei and electrons are es¬ 
tablished in an energy absorbing condition at an 
exponential rate whose time constant is Ti. In five 
time constants, essentially all of the nuclei or free 
electrons are biased for energy absorption and 
they are in thermal equilibrium with their sur¬ 
roundings called the lattice. Values of T, range 
from tens of nanoseconds to thousands of seconds 
over most of the ranges of nuclei, free electrons, 
and material property variations. When electro¬ 
magnetic energy is fed into these biased nuclei or 
free electrons, in the proper direction, at the 
proper frequency and of the proper magnitude, 
the biased nuclei or free electrons will absorb ener¬ 
gy and become out of thermal equilibrium with 
their surroundings. When out of thermal equilibri¬ 
um with their surroundings, energy will flow from 
the nuclei or free electrons to the surroundings ex¬ 
ponentially at a rate of T|. If energy is fed in at a 
rate faster than the nuclei or free electrons lose 
energy to the surroundings, they, in time, become 
saturated. When the energy is fed in at a lower rate 
than it is lost, energy will continue to be absorbed 
by the nuclei or free electrons and the rate of 
energy absorption is proportional to the volume 
concentration of nuclei or free electrons. There¬ 
fore, a quantitative analysis can be performed be- 


372 


low saturation. When energy is fed in continu¬ 
ously at a level either below or above saturation, 
the technique is called the steady-state technique. 

A transient technique can also be used where the 
radiofrequency energy is pulsed. It was found that 
at equilibrium, the hydrogen nuclei or free elec¬ 
trons are aligned parallel and antiparallel to the 
applied bias field direction. There are a few more 
per million parallel than antiparallel so that all of 
the nuclear magnetic moments at equilibrium sum 
to a small magnetic moment aligned parallel to the 
bias field. When pulses of radiofrequency energy 
are fed into the system at energy levels above satu¬ 
ration, all of the nuclei will precess or rotate 
around the direction of the applied radiofre¬ 
quency magnetic field. That means that the resul¬ 
tant magnetic moment also rotates around the ap¬ 
plied radiofrequency field. The rate of rotation in 
radians per second is directly proportional to the 
strength of the radiofrequency field. By control¬ 
ling the length of time the radiofrequency pulse is 
applied, the angle through which the resultant 
magnetic moment is rotated can be controlled. If 
one stops at 90°, 180° or 270°, the nuclei or free 
electrons are out of equillibrium with their sur¬ 
roundings and they lose energy to their surround¬ 
ings at the Ti rate, so that in a time equal to 5T,, 
almost all of these pulse-rotated magnetic mo¬ 
ments have returned to equilibrium which is align¬ 
ment with the bias field from which they can be 
rotated again. 

When the nuclei are rotated 90° and the radio¬ 
frequency pulse is removed, in addition to the ex¬ 
ponential return-to-equilibrium at the T] rate, 
there is also a dispersion of the magnetic moment 
vectors at a rate of T 2 . As was described before, at 
equilibrium, there are more magnetic moments 
aligned parallel to the field than antiparallel to the 
field, giving the net nuclear magnetic moment 
which is rotated by the radiofrequency pulse. 
When the net nuclear magnetic moment is a 90° 
and free of the radiofrequency pulse, it then pre- 
cesses around the direction of the bias field at a 
rate dependent upon the intensity of the magnetic 
field. Each nuclear moment is going to have a dif¬ 
ferent magnetic field at its position because of in¬ 
homogeneities in the bias magnetic field over the 
finite sample volume and because of internal mag¬ 
netic fields from neighboring nuclei with magnetic 
moments. The magnetic moment vectors, for each 
nucleus or for a small group of nuclei, can now be 
considered to precess at different rates because 
they are in different magnetic fields and the pre¬ 


cession rate is directly proportional to the bias 
field. Therefore, they tend to disperse and fan out 
rather than continue to act as a single net vector. 
Thus, the vector summation of these magnetic 
moments starts out at the net value at the end of 
the 90° pulse and then decreases exponentially, at 
a rate of T 2 , until at a time equal to 5T 2 , the nu¬ 
clear magnetization is zero in the plane perpendi¬ 
cular to the direction of the applied bias field. 

As described above, there are two decay rates or 
relaxation times associated with the transient nu¬ 
clear magnetic resonance technique, Ti and T 2 . 
The value of T, describes the thermal coupling be¬ 
tween the resonating nuclei and their surroundings 
sometimes called the lattice. The better the coup¬ 
ling, the shorter the value of Ti. The value of T 2 
describes the inhomogeneity of the bias magnet, 
and the magnetic influence between neighboring 
resonating nuclei. T 2 is always smaller than Ti. 
From the values of T, and T 2 , the Debye relaxation 
time can be calculated. Thus,from a knowledge of 
Ti and T 2 , information relating to the surround¬ 
ings of the resonating nuclei can be obtained. 

Two types of transient NMR signals are usually 
used: (1) a free induction decay following a 90° 
pulse, and (2) an echo following dual pulse se¬ 
quences such as: (a) two 90° pulses, (b) a 90° 
pulse followed at a time T| by a 180° pulse, or (c) a 
180° pulse followed at a time T by a 90° pulse. 
The transient NMR signals following a single 90° 
pulse and a dual 90 °-180° pulse sequence are 
given in Figures la and lb. The NMR signal in 
Figure la is called the free induction decay of FID. 
The NMR signal in Figure lb is called the spin 
echo. 



Free Induction Decay 
Type NMR Signal 


time 


a. Free Induction Decay 


90° 180° 






Echo Type 




y / 'V 

NMR Signal 

) 

1 

i ^ 
2*1 

^ time 


b. Spin Echo 


Figure 1. Two types of transient NMR signals, a. Free induc¬ 
tion decay following a single 90° pulse b. Spin echo following a 
dual 90°-180° pulse sequence. 


373 












With either method, steady-state or transient, 
signals can be obtained which are proportional to 
the number of nuclei or free electrons in the vol¬ 
ume being sampled. This gives quantitative anal¬ 
yses. The phenomenon occurs at a ratio of fre¬ 
quency to magnetic bias field intensity which is 
different for the nuclei of each isotope with a nu¬ 
clear magnetic moment and for free electrons. For 
example, the magnetic resonance phenomenon for 
hydrogen nuclei occurs at 4257.6 Hz per Gauss. 
For free electrons, resonance usually occurs at 2.8 
x 10 6 Hz per Gauss. Specific frequencies for the 
nuclei of specific isotopes can give quantitative 
analyses for isotopes and elements. 

Using the transient mode of operation with the 
hydrogen nuclei and the steady-state mode for 
free electrons, many measurements on explosives 
and propellants have been made. The results of 
these measurements are given in the following sec¬ 
tion. 

IV. NUCLEAR MAGNETIC RESONANCE 
SIGNALS IN MATERIALS 

Because there is more restriction to molecular 
motion in solids than in liquids, the value of T 2 for 
the hydrogen transient NMR signal from a liquid 
should be greater than the T 2 from a solid. Thus, 
in a mixture composed of a liquid and solid, the 
hydrogen transient NMR signal will have two 
components: one with a short T 2 from the hydro¬ 
gen in the solid and one with a longer T 2 from the 
hydrogen in the liquid. If the liquid is absorbed or 
adsorbed by the solid, then the T 2 of the absorbed 
or adsorbed liquid will be shorter than if the liquid 
were free. An example of a mixture with no liquid 
absorption is sand and water. An example of a 
mixture with liquid absorption is starch and water. 
There is no perceptable change in the T 2 of the 
water when a small amount of sand is added. The 
change in T 2 is small even when the weight of the 
sand may be ten times the weight of the water. 
However, there is a large change in the T 2 of the 
water when a small amount of starch is added. 
The difference is that starch is a material which 
absorbs or adsorbs the water and thus increases its 
effective viscosity or lowers the relative motion of 
neighboring hydrogen nuclei and thereby reduces 
the value of T 2 . Therefore, the value of T 2 de¬ 
creases linearly with increasing viscosity when 
plotted on a log-log scale. 

The explosives and propellants of interest will 
contain solids and liquids. In some of the mix¬ 
tures, the only liquid will be water. In other mix¬ 


tures, there are liquids which are one or more of 
the desired components. The hydrogen transient 
NMR signal from these materials can be used to 
measure moisture if the signal component from 
the hydrogen in the water is separated from the 
signals from the hydrogen in the remainder of the 
components. This can be readily accomplished if 
the T 2 values for all of the components are quite 
different. The closer they are to each other, the 
more difficult is the separation. The signal separa¬ 
tion problems can best be demonstrated by the sig¬ 
nals from some of the explosive and propellant 
materials of interest. The signals used will be from 
black powder, M-10 type propellant, T-36 type 
propellant, RDX, TNT, Composition B, and Type 
C-4 plastic explosive using RDX. 

A. Signals from Black Powder 

A representative hydrogen transient NMR free 
induction decay type signal from black powder is 
given is Figure 2. The black powder should have 
hydrogen in only the water, but it was found that 
there was a residue of incompletely pyrolyzed hy¬ 
drocarbon or hydrogen-containing material re¬ 
maining in the charcoal. Therefore, in Figure 2 
there are two hydrogen decay curves comprising 
the hydrogen free induction decay signal from the 
hydrogen in black powder. The one with the fast¬ 
est decay rate comes from the hydrogen in the in¬ 
completely pyrolyzed material in the charcoal and 
that component is labeled “solid” in Figure 2 
since that signal came from the hydrogen in the 
solid part of the black powder. The second com¬ 
ponent in Figure 2 has a much smaller amplitude 
and a much longer decay rate and it comes from 
the hydrogen in the water or the liquid part of the 
black powder. Since these signals are exponential 
type decay signals, a measurement at any time on 
their decay can be used to give the initial value at 
time equal to zero if the decay rate is known. For¬ 
tunately, the decay rates for the solid and liquid 
^components were known and were functions of 
only the temperature. Therefore, the signal pro¬ 
portional to the total hydrogen in the black pow¬ 
der sample could be determined by measuring the 
amplitude of the signal in Figure 2 at time “A” 
between 12 and 15 microseconds. The liquid com¬ 
ponent amplitude will need to be measured when 
the solid component has decayed to essentially 
zero. This occurs at time “B” in Figure 2 between 
55 and 65 microseconds. Now we have two 
signals, one proportional to the total hydrogen in 
the solid plus the liquid at around 13.5 micro¬ 
seconds and a second proportional to the liquid 


374 


signal at around 60 microseconds. To compare the 
two amplitudes, the liquid at 13.5 microseconds 
must be calculated. Since the decay time is known, 
this means nothing more than multiplying the 
value at 60 microseconds by the value to bring the 
time to 13.5 microseconds. When this is done, 
then values can be used to find the percent mois¬ 
ture on either a dry or wet basis. 

B. Signals from Type M-10 Propellant 

The hydrogen transient NMR signal from Type 
M-10 propellant is given in Figure 3. The solid sig¬ 
nal component has a different shape from the 
solid signal component in black powder. However 
changed the shape, the solid plus liquid value 
amplitude can be measured at time “A” or be¬ 
tween 12 and 15 microseconds while the liquid 
component can be determined at time “B” be¬ 
tween 55 and 65 microseconds. This is possible be¬ 
cause, even though the shape of the solid signal 
changed, it had still decayed to an insignificant 
value by 60 microseconds. 

To further investigate this possibility, a signal 
was recorded with the oscilloscope amplification 
10 times higher. The signal shown in Figure 4 was 
obtained. The solid plus liquid component was 


o 

> 

c 


nj 

C 

oc 

Z 

aZ 

S 

Z 



Figure 2. Free induction decay type hydrogen transient NMR 
signal from black powder at 30 MHz. 


Q0 



Figure 3. Free induction decay type hydrogen transient NMR 
signal form M-10 material at 30 MHz. 


Solid + Liquid 



Figure 4. Free induction hydrogen NMR signal from M-10 
type material at 30 MHz. 


added graphically to keep the perspective. The li¬ 
quid decay has only one component since it has 
only one exponential in the decay curve. There¬ 
fore, the measurement of moisture in Type M-10 
propellant can be accomplished with the same sim¬ 
ple procedure as was used with black powder. 

c. Signals from Type T-36 Propellant 

The normally observed hydrogen transient 
NMR signal from Type T-36 material is given in 
Figure 5. When the amplification of the oscillo¬ 
scope is doubled, and the time scale is lengthened 
by 20 times, the signal from T-36 appears as 
shown in Figure 6. The T-36 material contains 
two liquids, ethyl centralite and water. The liquid 
amplitude at 60 microseconds contains compo¬ 
nents from the decays from both liquids. To sepa¬ 
rate the two components, the voltage proportional 
to the hydrogen in the liquid with the longest de¬ 
cay rate should be measured at a time when the 
component from the other liquid has decayed to 
an insignificant value. It is most probable that the 
component with the longest decay rate is ethyl cen¬ 
tralite, at a concentration of 1.5%. It is most 
probable that its concentration can be measured at 
around 200 microseconds, at which time the mois¬ 
ture signal component should have decayed to in¬ 
significance. The three measurements at the three 
different times (13.5 microseconds, 60 microsec¬ 
onds, and 200 microseconds) can be used to deter- 


375 













mine the percent moisture again without weighing 
the sample: at 13.5 microseconds, solid plus both 
liquids; at 60 microseconds, both liquids; at 200 
microseconds, the second liquid. The second liq¬ 
uid subtracted from both liquids give the first liq¬ 
uid. When both are divided by the value at 13.5 
microseconds, the hydrogen ratios are obtained. 
The hydrogen ratios are converted into moisture 
percentages on a weight basis through the use of 
the proper conversion factors. 

D. Signals from RDX Type Explosive 

The free induction decay type signal from RDX 
is given in Figure 7. The signal component from 
the hydrogen in the solid RDX is labeled in Figure 
7. There appear to be two other signals between 20 
and 50 microseconds and 70 and 90 microseconds. 
These are not signals from another source but are 
due to Lowe-Norberg or “solid” beats from the 
hydrogen in the solid RDX. The water content of 
the sample used for Figure 7 was below 0.25% but 
it was never measured with the usual oven or titra¬ 
tion techniques because only one sample was 
available and it had to be preserved. It would ap¬ 
pear, however, that moisture measurements in 
RDX would be much like the measurements with 
M-10 and black powder. The two measurements 
would be made at 13.5 and 60 microseconds. The 
moisture value would be calculated through the 
use of the appropriate conversion constants. 

E. Signals from TNT Explosives 

7. Signals from Solid TNT 

The free induction decay type hydrogen transi¬ 
ent NMR signal from the TNT type explosive is 
given in Figure 8. When the NMR signal from 
TNT in Figure 8 is compared with the NMR signal 
from RDX in Figure 7, it can be concluded first 
that the decay rate for TNT is slower than the de¬ 
cay rate for RDX. The longer decay rate means 



Solid + Liquid 



Figure 6. Free induction hydrogen NMR signal from T-36 
type materials at 30 MHz. 

that the signal from the water must be taken at a 
time later than 100 microseconds. 

It can be concluded secondly from the above 
comparison, that the total signal, solid plus liquid, 
should be measured slightly later for TNT than for 
RDX, or between 15 and 18 microseconds. 

Here again, as for other materials, the percent¬ 
age moisture can be determined from two meas- 


O) 



Figure 7. Free induction decay type hydrogen transient NMR 
signal from RDX at 2.5 MHz. 



Figure 5. Free induction decay type hydrogen transient NMR 
signal from T-36 material at 30 MHz. 


376 


Figure 8. Graph of the tree induction decay type of hydrogen 
transient NMR signal from TNT. 





















urements of the amplitude of the signal from TNT 
in Figure 8. One measurement should be centered 
at 16.5 microseconds for the solid plus liquid (wa¬ 
ter) value and one at 110 microseconds for the liq¬ 
uid (water) value. These two values can then be 
used as previously presented to calculate the per¬ 
centage moisture once the conversion factor has 
been determined from hydrogen transient NMR 
measurements on many samples of TNT having 
moisture values spread over the expected range. 

2. Signals from Melted TNT 

Using a small sample available at SwRI, nuclear 
magnetic resonance measurements were made on 
melted TNT. The sample of TNT was melted in 
boiling water and inserted into the laboratory type 
transient NMR system at SwRI. Sequential photo¬ 
graphs of the transient NMR signals were made as 
the TNT solidified. The results are reproduced in 
Figure 9. No attempt was made to measure the 
temperature of the TNT as it cooled undisturbed 
in the apparatus. The transient NMR signals ob¬ 
served and pictured are the free induction decay 
responses described previously. In this laboratory 
NMR system, the magnet inhomogeneity effect is 
smaller than the T 2 of the material and the signals 
display the true spin-spin relaxation times, T>, of 
the solid and liquid components of the TNT as it 
changes from the melted to the solid condition. 

The free induction decay response in Figure 9a 
is for the TNT just after melting. By measuring 
and comparing the amplitudes of the response at 
appropriate points (illustrated by A and B in Fig¬ 
ure 9a), it may be seen that the percent liquids at 
this time is (3.6/4) 100 or 90 percent. After 15 
minutes, the percent liquid is (1.5/4) 100 or 
37.5%. After 20 minutes, the percent liquid has 
dropped to (0.6/4) 100 or 15%. After 23 minutes, 
the percent liquid is (0.1/4) 100 or 2.5%; see Fig¬ 
ures 9b, 9c, and 9d. 

In Figure 9, as the amount of liquid decreased, 
the total signal, the solid plus liquid, or the ampli¬ 
tude of the sharply peaked signal between zero 
and 0.2 milliseconds, did not change in amplitude 
but stayed fixed at 4 volts. This means that the 
transient NMR “sees” the total hydrogen in the 
sample, solid plus liquid. It also separately “sees” 
the hydrogen in the liquid. The graphs in Figure 9 
also show that the amount of solid is obtained 
simply by subtracting the voltage proportional to 
the hydrogen in the liquid TNT from the voltage 
proportional to the total hydrogen in the sample 
solid plus liquid. To obtain the total hydrogen 
(solid plus liquid) from an NMR response like 


those in Figure 9, the signal amplitude would be 
sampled as quickly as possible (10 to 20 microsec¬ 
onds) after the end of the 90° radiofrequency 
pulse. For the liquid component, the signal ampli¬ 
tude would be sampled as quickly as possible after 
the solid signal component has decayed to near 
zero level. As may be seen in the examples, the op¬ 
timum time for sampling the liquid component is 
on the order of 0.2 milliseconds after the start of 
the 90° pulse. 

F. Signals from Composition B Explosive 

Composition B is a mixture of 60% RDX, 39% 
TNT and 1% wax for a desensitizer. The free in¬ 
duction decay type of hydrogen transient NMR 
signal from Composition B is given in Figure 10. It 
appears to be a combination of Figures 8 and 9 in 
that there appear to be two components; one with 
a rapid decay like RDX and one with a longer de¬ 
cay like TNT. The signal from the wax and the wa¬ 
ter do not stand out in the signal in Figure 10. 
Therefore, in order to determine where in time to 
make the amplitude measurements on the TNT 
free induction decay signal to enable the calcula¬ 
tion of the moisture percentage without weighing 
the sample, many NMR measurements will need 
to be made on many samples with moisture values 
spread over the range of interest. From these 
many measurements can be obtained the conver¬ 
sion constants to convert the voltage ratios to per¬ 
cent moisture. 

G. Signals from Type C-4 Plastic Explosive 

The free induction decay type of hydrogen tran¬ 
sient NMR signals from RDX base Type C-4 plas¬ 
tic explosive is given in Figure 11 on the same time 
scale (100 microseconds) as most of the other sig¬ 
nals previously presented. Type C-4 explosive has 
both solid and liquid components as shown in Fig¬ 
ure 10. The measurement signals in Figure 10 were 
made at 2.5 MHz while the signals from the other 
explosives, except for RDX, were made at 30 
MHz. Therefore, there is more noise on the signal 
from C-4 than from the other explosives at 30 
MHz. The signal from C-4 has more noise than 
the RDX at the same frequency because the sam¬ 
ple of C-4 was smaller than the sample of RDX. 

Type C-4 is composed of 91% RDX, 2.1% 
polyisobutylene, 1.6% motor oil, and 5.3% 
di(2-ethylhexyl) sebacate. There are thus more liq¬ 
uids than the one, water, an impurity, to be meas¬ 
ured. All of the liquid signal, not just the first 100 
microseconds, is displayed in Figure 12. An expe¬ 
rienced observer of free induction decay signals 


377 



a. TNT Just After Melting 
Solid Plus Liquid - 4 

Liquid = 3. 6 
Solid =0.4 



1 


Time in Milliseconds 


3 3 
> 


32 

be 

•••* 

W 


1 


Solid 


Liquid 


* 


1 


Time in Millisecond* 


b. TNT After Cooling 15 Minutes 
Solid Plus Liquid = 4 

Liquid = 1.5 
Solid =2.5 


c. TNT After Cooling 20 Minutes 
Solid Plu8 Liquid = 4 

Liquid =0.6 
Solid = 3. 4 


d. TNT After Cooling 2 3 Minutes 
Solid Plus Liquid = 4 

Liquid = 0. 1 
Solid =3.9 


Figure 9. Free induction decay NMR signals from melted TNT as it cooled and solidified. 


would conclude that there are two or more expo¬ 
nential decays comprising the liquid decay signal, 
since it is a straight line for more than 3000 micro¬ 
seconds (3 milliseconds). 

In order to use NMR to measure the amount of 


moisture in Type C-4 explosive, the measurement 
times and conversion factors must be determined 
by performing NMR measurements on a signifi¬ 
cant number of samples of C-4 having moisture 
values over the range expected, or from 0.1% to 
1 %. 


378 


















Figure 10. Graph of the free induction decay type of hydrogen 
transient NMR signal from Composition B. 


Amplitude of 



Figure 11. First 100 microseconds of the free induction decay 
type hydrogen transient NMR signal from C-4 (RDX Base) at 
2.5 MHz. 


Amplitude of Solid + 
Liquid =1.2 Volts 


o 

> 

c 

• H 

0) 

•v 

B 

Oh 

£ 

c 

(0 

d 

bfl 

w 



Amplitude of Solid 
Component 

Amplitude of Liquid 
Component = 0. 78 Volts 


Time in Microseconds 


proper positions in time are found to take the data 
and when the proper conversion constants are 
used to convert voltage ratios to weight percent 
concentrations. 

Hydrogen transient NMR signals from the 
M-55 detonator mixture and the three type-A 
compositions were not presented because samples 
have not been available in previous projects. How¬ 
ever, the compositions of these materials are not 
significantly different from the compositions of 
the materials whose hydrogen transient NMR sig¬ 
nals have been presented. That is, the hydrogen 
transient NMR signals from compositions A-2, 
A-3, and A-4 should be similar to the signals 
from Composition B since the type-A composi¬ 
tions are mixtures of more than 90% RDX and 
densitizing wax which have been pressed at 3000 to 
12,000 psi. Therefore, the type-A compositions 
contain essentially two solid components with on¬ 
ly one liquid component, water. 

In the M-55 detonator mixture, all of the com¬ 
ponents of the mixture are solids and any liquid 
present should be water. Therefore, the hydrogen 
transient NMR signal from the M-55 detonator 
mixture should not be much different from the 
signal presented from M-10. If this assumption 
holds true, then moisture measurements in M-55 
detonator mixtures could be made by sampling the 
signal voltage at two times similar to the proce¬ 
dure described for M-10. Of course, the two 
measurement-time values may be different from 
the M-55 detonator mixture and different conver¬ 
sion constants may need to be used. The values of 
measurement times and conversion constants will 
need to be determined from hydrogen transient 
NMR measurements on samples of M-55 detona¬ 
tor mixture with known values of moisture over 
the range of interest. 


Figure 12. All of the free induction decay type of hydrogen 
type transient NMR signal from C-4 (RDX Base) at a 2.5 
MHz. 

H. Summary from NMR Signals in Explosives 

The materials of interest are RDX, TNT, Com¬ 
position B, M-55 detonator mixture, C-4, A-2, 
A-3, A-4, black powder, T-36 and M-10. Hydro¬ 
gen transient NMR signals have been shown for 
all of the above materials except the M-55 detona¬ 
tor mixture, A-2, A-3 and A-4. All of the data 
presented indicates that the hydrogen transient 
NMR signals can be used to determine the mois¬ 
ture content, on a weight percent basis, when the 


V. ELECTRON MAGNETIC RESONANCE 
SIGNALS IN MATERIALS 

Several types of explosives and propellants were 
scanned with an electron magnetic resonance spec¬ 
trometer operating at approximately 9,600 MHz 
in a magnetic field of 3400 Gauss. No free electron 
signal was obtained from RDS, TNT, Composi¬ 
tion B, or Composition C-4. 

A very strong free electron signal was obtained 
from black powder as demonstrated by the record¬ 
ed signal given in Figure 13a. A much weaker free 
electron signal was obtained from smokeless pow¬ 
der as shown by the signal in Figure 13b. The 
smaller signal from smokeless powder is caused by 


379 















the much lower concentration of charcoal in 
smokeless powder where it is used only as a glaze 
on each grain. If the same amount of black pow¬ 
der and smokeless powder is used, the free elec¬ 
tron signal from the black powder is about 250 
times that from the smokeless powder. 

The free electrons in the charcoal are caused by 
the pyrolysis. Broken bonds are caused in the large 
hydrocarbon molecules which result in an electron 
being set free. This free electron will be trapped in 
a potential energy well somewhere in the material 
where it will remain. Since the energy needed to 
bring the free electron out of the well is larger than 
its thermal energy, the free electron remains in the 
well and can be detected by the electron magnetic 
resonance spectrometer. If the charcoal were heat¬ 
ed at a temperature higher than that necessary to 
bring the free electron out of its well, it could be 



a. Black Powder (Dupont FF^ Superfine 

Black Rifle Powder) 

Quantity: 1 Flake 

Gain: X10 

Frequency: ~ 10 GHz 


lost by pairing with another and reduce the free 
electron magnetic resonance signal. 

VI. SPECIALIZED NMR AND EMR 
INSTRUMENTATION 

A. Background 

Work with NMR and EMR by most investiga¬ 
tors in the past has usually been laboratory studies 
with small samples and large, delicate apparatus. 
The sample to be studied is placed in the detection 
coil located in a large magnet, and by careful ad¬ 
justment and utilization of the system, excellent 
NMR data can be obtained. Data are most com¬ 
monly presented in graphical form. Typical labo¬ 
ratory NMR instrumentation will accommodate 
samples with a maximum diameter of a centimeter 
or two and a maximum length of two or three cen- 



b. Smokeless Powder (Dupont 
IMR -3031) 

Quantity: 10 grains 

Gain: X100 

Frequency: ^ 10 GHz 


Figure 13. ESR response of black and smokeless powder. 


380 



























































































































































































































































timeters. In many cases, where high resolution 
measurements are required, the maximum allow¬ 
able sample size is even smaller. Common labora¬ 
tory type EMR equipment imposes even more 
stringent limitations on sample size and shape. 
Again, the equipment is quite large compared to 
the allowable sample size, requires critical adjust¬ 
ment, and is also quite delicate. By careful adjust¬ 
ment of the instrument, however, excellent results 
can usually be obtained in a graphical form. These 
laboratory type magnetic resonance instruments 
are excellent for the study of the characteristics of 
those materials where a representative sample is 
available in a sufficiently small size. A selection of 
instruments of these types are available and rou¬ 
tinely used at Southwest Research Institute. These 
laboratory instruments are suited for laboratory 
studies of the chemical characteristics but would 
not be suited for use in field, industrial, or critical 
environments. On the basis of the prior experience 
gained at SwRI in the design and fabrication of 
advanced NMR and EMR systems, however, the 
development of specialized systems that would be 
entirely suitable is considered to be both feasible 
and practical. 

Development of advanced NMR and EMR in¬ 
strumentation systems to meet the special require¬ 
ments of a variety of difficult measurement, detec¬ 
tion, and control applications has been a major 
activity at Southwest Research Institute for the 
past 28 years. A number of NMR instruments 
have been developed for accurate quantitative 
measurements of particular constituents, such as 
moisture, in a variety of products and base mate¬ 
rials. Systems which will accommodate samples up 
to 14 x 23 inches in cross-section, which have ef¬ 
fective sample volumes of up to 5,000 cubic 
inches, and which are suitable for the detection 
and measurement of the NMR response from solid 
as well as liquid materials have also been devel¬ 
oped. Other NMR systems have been developed 
for measurements on samples located outside the 
physical extent of the apparatus, such as is re¬ 
quired, for example, for sensing buried materials. 
In addition, unique discriminating techniques 
have been developed to permit the use of NMR to 
detect small quantities of particular compounds of 
interest even in the presence of large quantities of 
background materials containing similar nuclei. 
These efforts have helped advance NMR from the 
status of a laboratory research and analytical tool 
to that of a practical measurement technique for a 
wide range of industrial, commercial, environ¬ 


mental, security and military applications. 

A number of specialized EMR systems have also 
been developed at SwRI and further efforts in this 
area are currently underway. This work has in¬ 
cluded the development of relatively low frequen¬ 
cy EMR systems which will accommodate large 
samples (several liters) and provide the very high 
sensitivity required for research purposes. Special 
detection methods have been developed to over¬ 
come the critical adjustment requirements of labo¬ 
ratory EMR systems and to allow practical detec¬ 
tion of the response from unstable, discontinuous, 
and moving samples. Other systems have been de¬ 
veloped for detection and measurement of the 
EMR response of charcoal and charcoal-based 
materials passing through an open aperture ap¬ 
proximately 0.5 meter wide and 0.4 meter high. A 
part of the current work is directed toward devel¬ 
opment of an EMR system for continuous, in situ 
measurement of the thickness of the layer of coal 
remaining over the substrate (shale or sandstone) 
during mining operations. 

The experience gained at SwRI in the previous 
programs has resulted in the basic science and 
technology, the creative staff and the facilities re¬ 
quired to efficiently and successfully apply the 
NMR and EMR techniques to unique situations. 
On the basis of this background, SwRI is well 
equipped to conduct the research studies and to 
develop the specialized instrumentation that are 
required to successfully apply the NMR and EMR 
methods to the material measurements of interest. 

B. NMR Equipment Possibilities 

The block diagram in Figure 14 gives the basic 
components needed to obtain a transient NMR 
signal, process it according to some requirement 



BASIC NMR APPARATUS 


Figure 14. Block diagram of typical transient NMR system. 


381 
















and display the processed data. Any magnetic res¬ 
onance device for hydrogen in explosives or pro¬ 
pellants would have the same basic block diagram. 
The sequencer, since this is a transient system, 
controls the timing of the radiofrequency pulses 
out of the transmitter, the gating of the receiver 
and the sampling of the signal amplitudes in the 
signal processor. The signal processor can then 
either display the signal amplitudes at two or three 
different times or it can process these two or three 
values to give the percentage amounts of each 
component containing hydrogen in the explosive 
or propellant. 

The detection head, composed of the detection 
coil or sample coil and the magnet in Figure 15, 
may be different in shape and size depending upon 
where it is to be used. For example, if the measure¬ 
ment of hydrogen in explosives or propellant is to 
be made on a flowing process stream, the detec¬ 
tion head shown in Figure 15 can be used. As the 
material flows through the sampled volume in the 
RF coil, the signal is taken from that section of the 
sample inside of the RF coil. The section of the 
process pipe inside the radiofrequency coil must 
be constructed from nonconducting materials hav¬ 
ing a low dielectric constant. 

The same shape and size of detection head as 
described above can also be used for nonflowing 
or stationary samples in test tubes or other con¬ 
tainers which will fit inside of the hole through the 
radiofrequency coil. 



H 



RF 

Sample 

Coil 


However, other measurement potentials exist if 
the detection head is made as drawn in Figure 16. 
When the magnet has a U-shape and the coil is a 
very short solenoid or a flat spiral, it is possible to 
make the conditions for the observance of the nu¬ 
clear magnetic resonance absorption at a distance 
from the magnet. The conditions required are: 

(a) The frequency, f 0 , of the radiofrequency 
field, Hi, and the intensity of the magnet field, 
Ho, obey the relationship 2 f 0 = yH 0 , where y is 
the gyromagnetic ratio which for hydrogen is 
26,751.29 radians per second per Gauss. For free 
electrons, y is 17.6 x 10 6 radians per second per 
Gauss. 

(b) The radiofrequency field, Hi, be at right 
angles to the direction of the magnetic field, H 0 , as 
shown in Figure 16. 

(c) The radiofrequency field, Hi, be of the 
proper intensity to cause the nuclei to be rotated 
through the angle desired, 90°, 180°, or whatever 
angle is chosen. If the steady-state is used, then H, 
will be less than that needed for saturation. 


RF Field 
Lines 



Figure 15. Sketch illustrating the sensing head concept for the 
magnetic resonance instrumentation. 


382 


Figure 16. Manifestation of the NMR detection head where 
the sensitive volume is outside of the magnet and RF coil con¬ 
figuration. 




















All of these conditions can be met in a specific 
volume at a specific distance from the detection 
head. Through the use of another magnet, smaller 
or larger than the U-shaped magnet in Figure 16, 
the field can be made relatively homogeneous over 
a small volume spaced a short distance of from Vi 
in. to 1 in. from the detection head. At the signal 
levels experienced from the EMR signals from 
black powder, a magnetic field of 100 Gauss (280 
MHz) should be sufficient for such EMR signals. 
Such a field is readily obtained at 1 in. from the 
magnet. For hydrogen nuclei in explosives and 
propellants, fields of 700 to 1000 Gauss are needed 
at distances of from Vi in. to 4 in. Therefore, hy¬ 
drogen and free electron signals could be obtained 
from explosives and propellants at distances of 
from Vi in. to 4 in. away from the magnet-detec¬ 
tion-coil system shown in Figure 16. To detect hy¬ 
drogen in moisture in concentrations of from 0.1 
to 1.0 percent, magnetic field values of 7000 Gauss 
are needed. 

The same detection head could detect the hydro¬ 
gen transient NMR signals from explosives and 
propellants as they are carried on an endless belt 


system. Such belts are usually in a shallow 
V-shape and the detection head could be mounted 
underneath the belt so as to detect the resonance 
of the hydrogen nuclei, not in the belt, but above 
the belt in the explosive or propellant carried on 
the belt from Vi in. to 1 in. away from the detec¬ 
tion head. 

Such detection heads could be mounted on a 
thin plastic section inserted in the wall of a large 
product pipe if it was inconvenient to use a thief 
tube run through the detection head configuration 
in Figure 15. Here again, hydrogen nuclei or free 
electrons would be detected at distances of from 
Vi in. to 4 in. away from the detection head into 
the product being carried through the pipe. 

Other detection head configurations are possi¬ 
ble, and this description is not meant to be an ex¬ 
haustive study of the possibilities. It does, how¬ 
ever, indicate some of the most obvious applica¬ 
tions of the two basic detection head configura¬ 
tions given in Figures 15 and 16. To the present, 
detection volumes 14 inches high, 24 inches wide 
and 30 inches deep have been accommodated in 
the magnet style in Figure 15. 


383 































EXPLOSIVE DETECTION 

























EXPLOSIVES DETECTION PROGRAM 
AT SANDIA NATIONAL LABORATORIES 


Frank J. Conrad 

Entry Control Systems Division 9252 
Sandia National Laboratories 
Albuquerque, New Mexico 87185 


ABSTRACT. A brief, general description of the Explosives Detection Program 
at Sandia National Laboratories is given. The six major topics of the program 
are: (1) Coated or Uncoated Metallic Preconcentrators; (2) a Derivatization 
Study; (3) a Portable Ion Mobility Spectrometer; (4) an Explosives Screening 
Portal; (5) Mass Spectrometer Development; and (6) an Explosive Vapor Genera¬ 
tor. 


INTRODUCTION 

Many organizations throughout the world are 
interested in developing an effective explosives de¬ 
tector; Sandia National Laboratories under the 
Department of Energy (DOE) is no exception. All 
organizations have requirements unique to their 
particular interest in the study of explosives detec¬ 
tion. Sandia is working on a program investigating 
vapor detection techniques for the sensing of 
explosives materials. This paper presents a brief, 
general description of that program. 

The six major topics of the program are: (1) 
Coated or Uncoated Metallic Preconcentrators; 
(2) a Derivatization Study; (3) a Portable Ion Mo¬ 
bility Spectrometer; (4) an Explosives Screening 
Portal; (5) Mass Spectrometer Development; and 
(6) an Explosive Vapor Generator. 

COATED OR UNCOATED METALLIC 
PRECONCENTRATORS 

A study was undertaken with the Department of 
Chemistry at the University of Texas (UT) at Aus¬ 
tin. The purpose of the study was a better under¬ 
standing of preconcentration on metallic sub¬ 
strates. Hopefully, the study will determine how 
explosives molecules are picked up, how they are 
held, how they are released when heated, and the 
temperature of release. 

In the initial experiment, a single crystal of 
platinum was dosed with TNT molecules. This 
was followed by Thermal Desorption Spectro¬ 
scopy (TDS) of the molecules. Auger Electron 


Spectoscopy indicated that the surface of the plati¬ 
num crystal was coated with carbon after the 
TDS. 

The researchers at UT found that the evolution 
of the explosive molecules from this preconcentra¬ 
tor occurs at temperatures much lower than ex¬ 
pected. When TNT is adsorbed at 100 K, there are 
two peaks in the desorption spectra. The first peak 
occurs below room temperature at 262-270 K and 
the second peak occurs just above room tempera¬ 
ture at 300-330 K. When studies were conducted 
at room temperature, the one remaining peak 
desorbed at the higher temperature and showed 
approximately the same characteristics as in the 
lower temperature work. This information indi¬ 
cated that metallic preconcentrators are much 
more efficient in environments cooler than room 
temperature. 

DERIVATIZATION STUDY 

Because explosives have low vapor pressures, 
they provide relatively few molecules with which 
to work. In addition, the tendency for explosives 
molecules to adsorb on surfaces makes it difficult 
to flow them through a tube to a detector. How¬ 
ever, forming a derivative of the molecules may 
make it easier to work with them. A study is 
underway to investigate this concept. It has been 
determined that a gas-phase reaction will probably 
be impossible; however, it is remotely possible 
that one could form a derivative while the mole¬ 
cules are in contact with a metallic surface. 


387 


PORTABLE ION MOBILITY 
SPECTROMETER (IMS) 

The IMS unit is one of the most sensitive devices 
for detecting TNT and DNT. Its ultimate sensitiv¬ 
ity for TNT is in the range of one part per trillion. 
The commercial IMS is a large laboratory instru¬ 
ment that requires a supply of zero air for the drift 
flow. PCP, Incorporated, has manufactured a 
more portable IMS with a special air purification 
system which obviates the need for gas bottles. 
The total flow of the gas enters the inlet. A part of 
the exit flow is passed through the purification 
system and then is reused as the drift gas. We find 
that the sensitivity of this “more portable” ion 
mobility spectrometer is equivalent to the labora¬ 
tory model and although it is till rather large, it is 
at least possible to place it in a 24 inch x 24 inch 
x 36 inch cart for transportation. Currently, 
small and more rugged IMS models are being in¬ 
vestigated. 

EXPLOSIVES SCREENING PORTAL 

A “Request for Quote” was sent to all known 
producers of commercial explosives detectors ask¬ 
ing them to submit portal configuration designs 
using their explosives detectors. A contract was 
placed with Xon-Tech, Incorporated, to build an 
explosives screening portal. In addition, a unit has 
been purchased from Ion Track Instruments, a di¬ 
vision of Analytical Instruments of England. A 
Sentex Portal has also been purchased. Compara¬ 
tive testing of these units using many different 
explosives is now being conducted. 

One of the problems in portal explosive detec¬ 
tion is that there are too few molecules to detect 
easily. When these molecules are further diluted 
by the air flow in the portal they can only be de¬ 
tected by an extremely sensitive detector. At the 
present time, commercial detectors have no prob¬ 
lem in detecting bomb quantities of dynamite; 
however, with this new series of portals, it is 
hoped the range of detection can be extended to 
include military grade TNT. If the range of detec¬ 
tion is extended to include most of the TNT 
samples, then only two major explosives of in¬ 
terest, RDX and PETN, will remain to be de¬ 
tected. 

MASS SPECTROMETER DEVELOPMENT 

When scientists are asked what kind of instru¬ 
ment they would use for detecting extremely small 
amounts of explosives vapors, almost invariably 


they mention a mass spectrometer. Those who 
have worked with the different applications of 
mass spectrometers will acknowledge that one of 
the major problems is finding an ion source that 
will not fracture these fragile molecules. The mass 
spectrometer has the sensitivity to detect a very 
small number of molecules; however, if the mole¬ 
cules are not transported into the mass spectrome¬ 
ter and ionized without degradation, there is no 
sensitivity. Negative ion formation is a possible 
means of ionization with low fragmentation. Since 
explosives molecules are highly electronegative, it 
should be possible, with low energy electrons, to 
form M~ ions of these molecules by resonance 
capture. Negative ionization should be desirable 
for at least two reasons: (1) most of the organic 
compounds in nature do not form negative ions, 
and (2) most of the explosives molecules should be 
in the M peak, and should thereby increase sensi¬ 
tivity. 

Currently, a number of ionization sources are 
being considered for use in a mass spectrometer- 
based explosives detector. Four of the sources are 
discussed in the following: 

1. A low energy electron ionization source was 
developed at Sandia. This source uses a heated 
filament in a retarding electrical field. This source 
gives large currents of electrons with energies in 
the range of 0.2 eV. Success with the source was 
limited because either the electrons were too ener¬ 
getic or the temperature of the heated filament de¬ 
graded the molecules. 

2. An Atmospheric Pressure Ionization (API) 
source was assembled to check its sensitivity for 
explosives molecules. The source has tremendous 
sensitivity. Most of the molecules are in the M 
peak as opposed to being spread over the whole 
range of masses as fragments. This source is still 
being evaluated. 

3. A corona discharge ionization source was de¬ 
signed and built by PCP, Incorporated, as a low 
energy electron ionizer for a mass spectrometer. 
One of these units was purchased and is being 
evaluated as another potential source. 

4. A photoelectron ionization source is being 
considered as a possible candidate source. Photo¬ 
electrons from photons interacting with a metal 
should be low in energy and at atmospheric pres¬ 
sure should moderate very rapidly. A photoelec¬ 
tron source is being purchased from Quantatec In¬ 
ternational, Incorporated, for evaluation. 

A “portable” mass spectrometer will be build 


388 


this fiscal year and will use one of the above ion 
sources. 

EXPLOSIVES VAPOR GENERATOR 

A calibrated explosives vapor source in needed 
for the evaluation of explosives vapor detectors. 
Problems with adherent vapors and accurate dilu¬ 
tion of the vapors to the parts per trillion range 
have hindered the development of such a vapor 
generator. In 1982, a contract was placed with 
XonTech, Incorporated, to produce two cali¬ 
brated vapor generators capable of delivering 
TNT vapors in concentrations ranging from 500 
parts per billion down to 3 parts per trillion. These 
two units are now being more accurately cali¬ 
brated in our laboratory. 

ACKNOWLEDGEMENTS 

The author wishes to acknowledge the following 


persons for invaluable help in the Sandia National 
Laboratories (SNLA) Program: Professor M. 
White, University of Texas, Dr. Henry Peebles, 
Principle Investigator, University of Texas; and 
the following, all from Sandia National Labora¬ 
tories: J. W. Rogers, preconcentrator work, 
Douglas C. Smathers, project leader and electrical 
work, Ms. Phyllis K. Peterson, vapor generator 
calibration, Pete J. Thoma, portal comparison, 
Richard Corn, mass spectrometer work and Jeff¬ 
ery B. McDowell, mechanical work. 

CONCLUSIONS 

This paper briefly describes the explosives de¬ 
tection program at Sandia National Laboratories. 
All vapor detection approaches that appear 
promising are being considered. 


389 































TEMPERATURE DEPENDENCE OF ADSORPTION 
EFFECTS OF EXPLOSIVES MOLECULES 


Phyllis K. Peterson 
Entry Control Systems Division 9252 
Sandia National Laboratories 
Albuquerque, New Mexico 87185 


ABSTRACT. Adsorption effects must be considered when selecting materials 
used for explosives vapor transport. Quartz, pyrex, Teflon, stainless steel and 
nickel adsorb explosives vapors at room temperature. The reduction in the adsorp¬ 
tive capabilities of these materials at elevated temperatures is discussed. Data were 
obtained by passing TNT, DNT, or PETN vapor through heat cleaned tubing. A 
gas chromatograph equipped with an electron capture detector was used for 
analyses. The temperatures needed to assure passage of explosives vapors range 
from 100-125°C for glass and quartz to 150°C for nickel, stainless steel, and 
Teflon. 


INTRODUCTION 

Explosives vapor detection can be hindered by 
the tendency of these vapors to be adsorbed on 
cold surfaces. Such behavior was first observed in 
our laboratory during the evaluation of an explo¬ 
sives detector equipped with a Teflon inlet tube. It 
was observed that the instrument was unable to 
detect low concentrations of TNT vapor until the 
instrument was first “conditioned” by exposure 
to a very high concentration of TNT vapor. Later, 
we encountered adsorption problems when using 
metal tubing to transport explosives vapors in a 
vapor generator. We learned that the easiest way 
to circumvent these adsorption problems was to 
heat the transport tubing. A comparative study of 
various materials was made to determine the tem¬ 
perature at which these materials must be main¬ 
tained in order to ensure efficient transport of ex¬ 
plosives vapors. The materials evaluated were 
pyres, quartz, Teflon, stainless steel, and nickel. 


Table 1. TUBING MATERIALS EVALUATED 


Material 

!4 inch OD* Stainless Steel 
14 inch OD Teflon (TFE) 

'/, inch OD Nickel 
!4 inch OD Pyrex 
!4 inch OD Quartz 


Source 

Supelco Cat 02-0527 
Supelco Cat #2-0533 
Supelco Cat #2-2709 
Sandia Glass Shop 
Sandia Glass Shop 


EXPERIMENTAL PROCEDURE 

Commercially available % inch and 14 inch out¬ 
side diameter (OD) tubing was used in this study. 
Table 1 lists the types of tubing evaluated. The 
tubing was cut so all samples had the same inter¬ 
nal surface area of 2.65 x 10 3 square meters 
(four square inches). Before evaluation, the tubing 
samples were degreased with solvent and heat 
cleaned at 250 °C. 

The clean tubing samples were placed in the 
oven of a Hewlett-Packard 5880 Gas Chromato¬ 
graph (GC) where they served as a direct link from 
a 150°C injection port to a 200°C electron capture 
detector. Optimum performance of the electron 
capture detector was achieved by using 95% 
argon/5% methane as the carrier gas with a flow 
rate of 40 ml per minute. 

A known nanogram quantity of explosive in 
acetone solution was injected into the tube while 
the oven was maintained at constant temperature 


Size 

0.53mm x 5.3mm ID** 
0.53mm x 5.8mm ID 
1,35m x 2.1 mm ID 
0.76m x 4mm ID 
0.76mm x 4mm ID 


*OD = outside diameter 

** ID = inside diameter 


391 



at or above room temperature. This temperature 
was held for three minutes after injection and this 
allowed the solvent to clear the detector. If the ex¬ 
plosive did not also pass through the detector 
within the three minute holding period, the GC 
oven was then heated to 200°C to drive off ad¬ 
sorbed explosive vapor. 

For all materials, the initial data points were 
collected at 25 °C using the aforementioned tech¬ 
nique. The temperature was then increased by 
25 °C increments until the explosive peak appeared 
during the initial three minute holding time. Then 
smaller increments of 5°C or 10°C were used until 
a temperature was reached when the explosives 
vapors would pass through the tubing with the 
solvent. 

Three explosives were used in this evalua¬ 
tion: Trinitrotoluene (TNT), Dinitrotroluene 
(DNT), and Pentaerythritol Tetranitrate (PETN). 
Purified samples were prepared at Sandia Nation¬ 
al Laboratories for this purpose. 

TNT and PETN are commonly used explosives 
which are difficult to detect because of their low 
vapor pressures at room temperature; at 25 °C 
TNT has a vapor pressure of 10 parts per billion 
and PETN has a vapor pressure of 10 parts per 
trillion. DNT is a higher vapor pressure impurity 
(750 parts per billion at 25 °C) found in TNT; 
DNT contributes to the detectability of impure 
TNT. 

RESULTS 

The data from this study are presented in Fig¬ 
ures 1 through 3. Two plots are shown for each ex¬ 
plosive; one shows percent retention versus tem¬ 
perature and the other shows retention time versus 
temperature. 

The study was originally designed to produce 


data fcr plotting percent retention versus tempera¬ 
ture. Preliminary studies with Teflon tubing indi¬ 
cated that the percent retention would decrease 
with increasing temperature and that retention 
time would be an uninteresting variable. However, 
this was not the case with other tubing materials. 
With some combinations, the percent adsorption 
remained at a high constant value while retention 
time decreased with increasing temperatures. 
Therefore, both plots are presented to give a better 
picture of adsorption-temperature relationships. 

In the Percent Retention versus Temperature 
Plots, the data are normalized with the amount of 
vapors adsorbed at 25 C assumed to be 100% ad¬ 
sorption. 

For the Retention Time plots, the time given is a 
total of the three minute holding time and and ad¬ 
ditional heating time at 20 C per minute. Reten¬ 
tion times over three minutes are not actual 
values, but these numbers can be used to calculate 
the temperature at which the adsorbed explosive 
was driven from the tubing sample. 

The plots show much variability with the differ¬ 
ent materials; this variability canno’t be predicted a 
priori. 

CONCLUSIONS 

Under laboratory conditions, tubing materials, 
such as, pyrex, quartz, Teflon, nickel and stainless 
steel were found to adsorb and retain explosives 
vapors. Our results suggest that glass and quartz 
should be heated to at least 100 C while Teflon, 
stainless steel, and nickel should be heated to at 
least 150 C in order to ensure the transport of 
TNT vapors. For the transport of PETN vapors, 
glass and quartz tubing should be maintained at 
an even higher temperature of 125 C. 


392 


RETENTION TIMES - MIN. % RETENTION 


TNT 

ADSORPTION/TEMPERATURE 



TNT 


RETENTION TIMES 



Figure 1. TNT adsorption characteristics on various tubing materials. 


393 


















RETENTION TIME IN MINUTES 


DNT 


ADSORPTION/TEMPERATURE 



DNT 

RETENTION TIMES 



Figure 2. DNT adsorption characteristics on various tubing materials. 


394 











RETENTION TIME IN MINUTES 


PETN 


ADSORPTION/TEMPERATURE 



PETN 

RETENTION TIMES 



20 40 60 


80 100 120 
TEMPERATURE °C 


140 160 180 


Figure 3. PETN adsorption characteristics on various tubing materials. 


395 



























































THE SORPTION OF EXPLOSIVES ON HUMAN HAIR 


D. F. Wardleworth andS. A. Ancient 
Royal Armament Research and Development Establishment 

Fort Halstead 


ABSTRACT. In the absence of bulk explosives, demonstration of illegal explo¬ 
sives involvement relies heavily on trace explosives contamination. In their most 
significant form traces will be closely associated with a suspect, for example on the 
hands. Such traces usually result from contact contamination, but experiments 
have shown that some common explosives constituents, for example ethylene gly¬ 
col dinitrate (EGDN) have a sufficiently high vapour pressure to contaminate near¬ 
by objects via the vapour-phase. This opens up a wide area of study, some aspects 
of which are considered in a separate paper. Such contamination could be expected 
to occur on clothing, exposed skin and head hair, and it is the latter which will be 
discussed. Preliminary studies indicated that thermal desorption (ie. heating con¬ 
taminated hair in a purge gas) gave variable recoveries of explosives vapour, and 
that adequate results were obtainable by solvent extraction despite some difficul¬ 
ties due to lipid. In subsequent experiments this recovery technique was used to 
study the influence of humidity, hair type and hair cleanliness on vapour uptake 
and persistence. The potential of hair contamination was assessed by exposing a 
volunteer to vapour from explosive and subsequently removing small hair samples 
for analysis. Identifiable traces of EGDN were recoverable for several hours after 
exposure. Aspects of this approach which would benefit from further work are in¬ 
corporation of a clean-up, a population contamination survey and an informed re¬ 
view of the legal implications. 


INTRODUCTION 

Many forensic laboratories regularly examine 
clothing, handswabs, surfaces in vehicles and 
other samples for explosives traces at or below the 
microgram level. Positive findings can generally 
be attributed to the contact transfer of solids or 
liquids either directly or indirectly, e.g. when con¬ 
taminated hands convey explosives to other sur¬ 
faces such as the edges of pockets. With certain 
explosives, such as gelignite, contamination by a 
different mechanism is possible owing to the emis¬ 
sion of small amounts of characteristic vapour 
which could be sorbed and retained by exposed 
surfaces. A familiar example of this effect is the 
retention of tobacco smoke by clothing and hair. 
Contamination of hair by this means was studied 
in the present work because of its novelty and po¬ 
tential. The only comparable study appears to be 
the work of Baumgartner on the deposition of the 
abused drug phencyclidine on hair during its in¬ 
gestion by smoking (Reference 1). The chemical 


species chosen for the present work were ethylene 
glycol dinitrate (EGDN) and nitrobenzene (NB). 

Hair presents some potential difficulties as an 
analytical substrate. Each fibre consists of an in- 
homogenous and complex mass of keratin fibres 
held in a keratin matrix (Reference 2), enclosed 
within a tough cuticle composed of up to ten 
layers of overlapping scales. The cuticle of animal 
fibres is known to form a barrier to molecules en¬ 
tering or leaving the fibre (Reference 3) and suc¬ 
cessful analysis of hair must either destroy it or al¬ 
low for its effects. Hair may carry cosmetics resi¬ 
dues and airborne dust in addition to natural 
secretions and cell scales, all of which could inter¬ 
fere with analysis. These problems have been en¬ 
countered in the analysis of drugs of abuse in hair 
(Reference 1,4) and in the analysis of chlorinated 
hydrocarbons deposited in hair during growth 
(Reference 5). In each instance solvent extraction 
was employed, the hair sometimes being ground 
up, and this recovery technique seemed a promis- 


397 


ing one to evaluate. Thermal recovery, demon¬ 
strated by Chrostowski, Holmes and Rehn while 
working with explosion debris (Reference 6), has 
been found to work successfully for EGDN and 
NB on substrates such as PVC (Reference 7) and it 
was decided also to evaluate this method because 
it yields extrcts free from involatile contaminants. 

EXPERIMENTAL 

Preparation of Hair Samples for Evaluation of 
Analysis 

A large, relatively homogenous batch of hair 
was produced by mixing hair from a men’s hair¬ 
dresser using a compressed air jet. Because of the 
difficulty of uniformly spiking a hair sample with 
a known amount of EGDN or NB, much of the 
analysis evaluation was performed on a compari¬ 
son basis using hair contaminated by exposure to 
the appropriate vapour. Various atmospheric con¬ 
centrations of EGDN or NB were generated in a 
15 1. bell jar using a perfusion tube containing 
EGDN or NB in conjunction with an exponential 
dilution system (Figure 1). Vapour concentrations 
in the jar were measured by drawing 500ml of air 
through a trap containing Tenax (R) and eluting 
sorbed EGDN or NB with 0.5ml ethyl acetate for 


later analysis. The final validation experiments re¬ 
quired samples of known composition and these 
were produced by adding 15 pi. of a hexane solu¬ 
tion of EGDN or NB to 2g of hair in random¬ 
ly-distributed 1 pi. increments. The spiked hair 
was left in a stoppered flask for three days to 
equilibrate before it was analysed. 

Analysis 

Solutions containing EGDN or NB were quanti¬ 
fied by gas chromatography (GC) with elec¬ 
tron-capture detection using a glass WCOT 
column, coated with SE30, 50m x 0.5mm id. This 
was fitted with a splitter which passed 10% of the 
0.5ul injection on to the column. The column tem¬ 
perature was 122°C and the nitrogen carrier flow 
rate was 1.5ml min '. An integrator operating in 
the peak-height mode gave accurate retention 
times. Standard solutions were made up in hexane 
to cover the range 50 to 500pg pi -1 , using NB 
(BDH microanalytical reagent) and EGDN 
(PERME Waltham Abbey). 

Thermal Recovery 

The hair sample of c 0.3g was placed in a glass 
test tube fitted with a modified Dreschel head 
(Figure 2) and the apparatus was kept at 95 °C for 



Figure 1. Exponential dilution system for exposing samples to known atmospheres. 


398 



























Figure 2. Apparatus for thermal recovery of volatile traces. 

up to 6h while a nitrogen purge (25ml min ') car¬ 
ried evolved vapour to a second tube containing 
toluene. In some experiments water was added to 
the sample before heating in order to enhance re¬ 
covery. Extracts were concentrated to 0.5-5ml by 
heating on a steam bath under a stream of air. 

Recovery by Solvent Extraction 

In initial experiments 0.7g portions of hair were 
extracted by soaking in 20ml hexane or toluene at 
20 °C for up to 96h and the solvent was removed 
by filtration and concentrated as described above. 
In subsequent analyses 0.3g of hair was extracted 
by soaking in 10ml of solvent at 55 °C for up to 
24h, and this method was used in the main experi¬ 
ments. In some instances the concentrated extracts 
were stored at — 18°C for 2h to freeze out co-ex- 
tracted lipid and the solutions were analyzed be¬ 
fore this re-dissolved. 

Sorption Studies 

The effects of hair type, ambient humidity and 
hair cleanliness on the amounts of EGDN and NB 
sorbed by hair were investigated. Because there 
are potentially many types of hair no comprehen¬ 
sive survey was attempted and instead one addi¬ 
tional type was studied, female hair which had 
been curled by permanent waving. ‘Clean’ hair 
was prepared by washing bulked male hair with a 
shampoo, rinsing three times in water and allow¬ 
ing it to dry on filter paper. Humidity during ex¬ 
posure was held either at 10% relative humidity 
(RH) or 90% RH (Figure 1). The vapour concen¬ 
trations studied ranged from 0.6 to 20mg m 3 and 
the exposure time for all samples was %h. After 
exposure hair samples were left in open air at ap¬ 
proximately 20°C and 50% RH and samples were 
analysed at intervals. 

Two larger-scale experiments were conducted. 


In the first, a dummy head was constructed by 
fastening bulked male hair on to a 1 litre flask 
using adhesive tape and the flask was heated to 
36 °C by water circulation and exposed to gelignite 
vapour for 3 /4h. The vapour source was removed 
from the room and samples wfcre analysed at inter¬ 
vals over the next few hours. 

In the final experiment a male subject was ex¬ 
posed to gelignite vapour for 3 /4h and 0.3g hair 
samples were removed for analysis over a period 
of four days. 

RESULTS 

Recovery Experiments 

The comparative experiments indicated that 
thermal recovery of EGDN was less efficient than 
solvent extraction (Table 1, experiment 1) and that 
no consistent improvement was attained by adding 
water (experiments 2 and 3). Because a general re¬ 
covery method was required thermal recovery of 
NB from hair was not examined and further work 
concentrated on solvent extraction. 

The results (Table 2) indicated that even at 55 °C 
an extraction time of at least 3h was required for 
efficient recovery of both EGDN and NB. There 
was no advantage in using toluene rather than hex¬ 
ane and so the latter was used in subsequent 
analyses because of its convenience and lower tox¬ 
icity. Grinding hair before extraction gave a re¬ 
duced recovery of EGDN and of NB. 

Effects of Hair Type, Cleanliness and Humidity 
on Vapour Sorption 

The amounts of EGDN and NB sorbed by hair 
under various conditions were not determined by 
measurement immediately after exposure because 
the concentration of sorbed material altered rapid¬ 
ly at that stage. Instead, samples from each ex¬ 
posed batch of hair were analysed at intervals of 
several hours and the 5-6 results so obtained were 
plotted as a graph of time versus log concentra¬ 
tion. A linear relationship was found for each set 
of results (e.g. Figure 3), indicating that the con¬ 
centration of sorbed material decayed according 
to first-order kinetics. By extrapolation the initial 
concentration C 0 was obtained for each experi¬ 
ment and this was used as a basis for comparing 
the effects of humidity etc. The decay constant or 
half-life t‘A was also calculated for each set of re¬ 
sults and its reliability was estimated by calculat¬ 
ing Student’s t and comparing it with tables of the 
t-distribution. C 0 , t'A and the statistical signifi¬ 
cance for each experiment are listed in Tables 3-5. 


399 














Table 1. RECOVERY OF EGDN FROM HAIR EXPOSED TO EGDN VAPOUR 


Sample Batch No. 

Recovery method 

EGDN recovered, ng mg- 1 

1 

thermal 0-3h 

0.6 


3-6h 

0.004 

1 

thermal 0-3h 

0.7 


3-6h 

0.008 

1 

hexane extraction, 

24h at 20 °C 

1.65 

2 

thermal 0-3h 
(2ml water added) 

2.6 

2 

hexane extraction, 

24h at 20 °C 

2.8 

3 

thermal 0-3h 
(2ml water added) 

0.4 

3 

hexane extraction 

96h at 20°C 

1.0 


Table 2. RATE OF SOLVENT EXTRACTION OF ADDED EGDN/NB AT 55°C 


Amount recovered 


Sample 
hair sample 
analyte added 

Extraction 

conditions 

Extraction time 

hours 

ng mg- 1 

as cumulative 

°7o of added 

amount 

EGDN, 9.0ng mg- > 

unground sample, 

0-1 

6.9 

76 


hexane 

1-3 

2.1 

100 



3-24 

0.5 

105 

EGDN, 9.0ng mg- 1 

ground sample, 

0-1 

4.2 

46 


hexane 

1-3 

1.6 

64 



3-24 

0.5 

64 

NB, 15ng mg- 1 

unground sample, 

0-1 

9.4 

62 


toluene 

1-3 

2.5 

79 



3-24 

1.0 

85 

NB, 15ng mg- 1 

ground sample. 

0-1 

6.1 

40 


toluene 

1-3 

2.2 

48 



3-24 

0.5 

51 

NB, 1 5ng mg- 1 

unground sample, 

0-1 

8.8 

58 


hexane 

1-3 

2.4 

74 



3-24 

2.3 

89 


400 









Table 3. SORPTION AND RETENTION OF EGDN AND NB BY UNWASHED MALE AND FEMALE HAIR 


Exposure vapour 
(Cone mg m- 3) 

Hair 

c„ 

ng mg- 1 

tVi 

h 

Level of significance 

P 

EGDN (1) 

Bulked male 

5.7 

15 

0.05 

EGDN (1 ) 

female 

5.1 

22 

0.01 

NB (2) 

bulked male 

3.7 

72 

0.1 

NB (2) 

female 

13.0 

43 

0.05 

NB (2) 

abraded bulked 

5.6 

98 

0.1 


male 





EGDN CONC ( LOG ngg 1 ) 



Figure 3. EGDN persistence in the hair of a volunteer. 


401 











The results in Table 3 suggest that the two types 
of hair studied had a similar affinity for EGDN, 
C 0 for each being c 5ng mg In contrast ap¬ 
preciably more NB was sorbed by the female hair 
than by the male hair and this effect was not re¬ 
produced by abrading male hair before exposure. 

The effects of washing also varied according to 
the chemical species sorbed (Table 4). There was 
no difference between the amounts of NB taken 
up by unwashed and washed bulked male hair, C 0 
for each being 13ng mg -1 , but unwashed bulked 


male hair sorbed 5.7ng mg' 1 of EGDN compared 
to only 2.6ng mg 1 of EGDN sorbed by washed 
hair. 

The ambient humidity during exposure affected 
sorption of both EGDN and NB in the same way, 
more vapour being taken up in high humidity than 
in low humidity (Table 5). The statistical signifi¬ 
cance of both sets of NB results was poor 
(P > 0.1) but the effect of humidity was consistent 
with the more reliable EGDN observations. 


Table 4. SORPTION AND RETENTION OF EGDN AND NB BY UNWASHED AND W ASHED MALE HAIR 


Exposure vapour 
(cone mg m~3) 

Pretrealmenl 

C„ 

ng mg- * 

{Vi 

h 

Level of significance 

P 

EGDN (1) 

Unwashed 

5.7 

15 

0.05 

EGDN (1) 

washed 

2.6 

36 

0.1 

NB (20) 

unwashed 

13.0 

38 

0.05 

NB (20) 

washed 

13.0 

48 

0.05 


Table 5. EFFECT OF AMBIENT HUMIDITY ON SORPTION OF EGDN AND NB BY MALE HAIR (SAMPLES EXPOSED 
TO 50% RH AFTER EXPOSURE) 

Exposure vapour 
(cone mg m-3) 

Humidity during 
exposure %RH 

C„ 

ng mg- 1 

XVi 

h 

Level of significance 

P 

EGDN (0.6) 

90 

1.2 

25 

0.05 

EGDN (0.6) 

10 

0.3 

56 

0.05 

NB (2) 

90 

3.7 

72 

>0.1 

NB (2) 

10 

0.7 

32 

>0.1 


402 






Persistence 

The decay half-lives from the small experiments 
(Table 3-5) are summarised in Table 6. The mean 
of the t '/2 values for EGDN was 28h and for NB 
the mean t '/2 was 51 h; using the t-test (with the 
Bessel correction for small number of results) this 
difference was found to be significant (p = o.o5). 

Table 6. SUMMARY OF DECAY HALF-LIVES 


Substance 

tVa hrs 

Level of 
significance 

EGDN 

15 

0.05 


22 

0.01 


15 

0.05 


36 

0.1 


25 

0.05 


56 

0.05 

NB 

72 

0.1 


43 

0.05 


38 

0.05 


48 

0.05 


72 

0.01 


32 

0.1 


EGDN persistence results from the experiments 
with the dummy head and with a volunteer yielded 
the reduced t Vi values of 7h (not significant at the 
p = 0.1 level) and 11 h (highly significant, p = 
0.01). The reduced t '/2 values was attributed to the 
higher hair temperature in these experiments. 

DISCUSSION 

At the commencement of this study it was sus¬ 
pected that any EGDN or NB taken up by hair 
would be sorbed at the fibre surface, perhaps dis¬ 
solved in a lipid coating. This simplistic picture is 
incorrect, as shown by the considerable time nec¬ 
essary for solvent recovery, i.e. at least 3h at 
55 °C, which is probably due to the slow migration 
of molecules from within the fibre to its surface. 
The increased thermal recovery obtainable by add¬ 
ing water also suggest retention within the fibre; 
presumably the high humidity cases the fibres to 
swell and increases the permeability of the cuticle. 
The enhanced amounts of vapour taken up during 
exposure in a high ambient humidity is also at¬ 
tributable to this effect. 

EGDN or NB could be retained in a lipid phase 
held within the fibre, but interaction with fibre 
keratin is also possible. If solution in a lipid phase 
were the principal mechanism the vapour pressure 
of EGDN and NB (EGDN 0.049mm Hg at 20°C 


(Ref 9); NB 0.22mm Hg at 20°C (from extrapola¬ 
tion of data in Reference 9)), would be reduced to 
Pc according to Raoults’ Law, 

Pc = XcPo 

where P 0 is the vapour pressure and x c is the con¬ 
centration of the sorbed species expressed as a 
mole fraction. Although much reduced, the 
vapour pressures of EGDN and NB would still 
bear the same relative volatility, ie NB would be 
the more volatile. NB would therefore be expected 
to be lost more rapidly from hair than EGDN, but 
the reverse was observed in practice, the mean t '/2 
for EGDN being 28h and the mean t'/i for NB 
being 51h. This suggests that the molecules inter¬ 
act with the hair fibre itself, NB binding more 
strongly than EGDN. The different effects noted 
with unwashed/washed hair and male/female can 
then be explained as follows: (1) EGDN is mainly 
held in the hair lipid phase, the amount of which is 
reduced by washing, and (2) NB is mainly held by 
hair keratin and female hair sorbed more NB by 
virtue of structural differences possibly induced 
by permanent waving. 

Persistence on live subjects has only been 
studied briefly using EGDN, and the half-life of 
1 lh obtained with EGDN suggests that hair analy¬ 
sis is potentially useful. Aspects which remain to 
be studied include sorption mechanisms, potential 
interferences and legal implications. 

Copyright © Controller, Her Majesty’s Sta¬ 
tionery Office London 1983. 

REFERENCES 

1. Baumgartner A M, Jones P R, Black C T: J 
Forensic Sciences, 26(3) 576-589 (1981). 

2. Robins C R: Chemical and Physical Be¬ 
haviour of Human hair, Van Nostrand Rein¬ 
hold Co (1979). 

3. Earland C: Wool—Its Chemistry and Physics, 
2nd edn; Chapman and Hall (1963). 

4. Valente D, Cassini M, Pigliapochie M, 
VansettiD : Clin Chem, 27 (11) 1952-3 (1981). 

5. Matthews H B, Domanski J J, Guttrie 
F E : Xenobiotica, 6 (7) 425-429 ( 1976). 

6. Chrostowski J E, Holmes R N, Rehn B W: 
Forensic Sciences, 21 (3) 611-15 (1976). 

7. Cashen S A, Wardleworth D F : unpublished 
results. 

8. Sch/essinger G G: Handbook of Chemistry 
and Physics, CRC Press (1973-74). 

9. Pella PA: Anal Chem, 38 (3) 1632-1637 
(1976). 


403 

























































A NOVEL METHOD FOR THE RECOVERY OF 
VOLATILE EXPLOSIVES TRACES 


D. F. Wardleworth andS. A. Ancient 
Royal Armament Research and Development Establishment 

Fort Halstead 


ABSTRACT. Although trace explosives contamination can sometimes be detect¬ 
ed with an explosives vapour detector, further positive identification is usually nec¬ 
essary. For reasons of practicality this will generally involve recovery of the explo¬ 
sives traces from the substrate, ideally without co-extracting other materials which 
could interfere with analysis. When recovering volatile explosives such contamina¬ 
tion can be minimised by employing high-temperature vapour-stripping, in which 
a purge gas transfers desorbed vapours to a suitable trapping arrangement. If rapid 
screening of several items such as clothing is required, or where the sample is l?rge, 
such as a vehicle, thermal recovery using conventional laboratory apparatus is in¬ 
appropriate, and to overcome this problem portable recovery equipment has been 
devised. This consists of a heated platen which is placed in contact with the sur¬ 
face, an air pump and a trap containing Tenax (R), a polymeric absorbent. In vali¬ 
dation experiments this device recovered ethylene glycol dinitrate (a constituent of 
commercial gelignites) and other explosives vapours from a variety of substrates. 
In most instances it was much more efficient than solvent-swabbing, the main al¬ 
ternative. With a sampling time of five minutes the limit of detection was 5 ng per 
square centimetre. At this level of sensitivity the forensic scientist can recover 
traces resulting from vapour-phase contamination, in addition to the contamina¬ 
tion resulting from contact or from explosion, and the technique has been success¬ 
fully used in a number of forensic cases. 


INTRODUCTION 

There are two basic situations in which trace 
analysis of explosives may arise. Post-detonation 
debris is examined to identify the type of explosive 
involved, and although quite large amounts of ex¬ 
plosive may be present, trace techniques are usual¬ 
ly required. Examinations also attempt to estab¬ 
lish whether there is any evidence linking suspects, 
or their clothing, premises and vehicles with the il¬ 
legal usage of explosives, and this too requires 
trace analysis. In either situation it is sometimes 
possible to obtain a rapid indication of explosives 
contamination using a suitable explosives vapour 
detector such as the Analytical Instruments AI70 
or the Pye PD3, but these can best be regarded as 
a potential shortcut in defining contaminated 
areas rather than as a substitute for analysis. At 
present chemical analysis requires extraction of 
explosives from a contaminated object, usually by 
solvent extraction or swabbing with cotton-wool 


and solvent. Provided suitable solvents are em¬ 
ployed these recovery techniques are applicable to 
a wide range of explosives, but they tend to give 
‘dirty’ extracts containing co-extracted material 
which may interfere with or prevent analysis. One 
answer is to incorporate a suitable clean-up, for 
example that of Douse (Reference 1), but a better 
alternative is to employ a clean recovery technique 
in the first place. If the explosives traces are vola¬ 
tile, as will be the case when the commonly mis¬ 
used gelignite explosives are involved, thermal re¬ 
covery is possible, and this has the enormous ad¬ 
vantage of yielding clean samples for analysis. 
This technique was first demonstrated by Chros- 
towski, Holmes and Rehn (Reference 2) who re¬ 
covered explosives such as TNT which had been 
added to sand by heating the mixture while draw¬ 
ing air through it. We have adapted the technique 
to permit semiquantitative analysis of samples 
containing nanogram amounts of ethylene glycol 


405 


dinitrate (EGDN), a constituent of gelignites, 
while for field use we have developed a portable 
recovery device which we refer to as the con¬ 
tact-heater. The contact-heat permits rapid recov¬ 
ery of volatile explosives and is particularly useful 
when examining large items such as an overcoat or 
a vehicle. 


THE CONTACT-HEATER 
Description 

This equipment consists essentially of a platen 
heated to 100 °C which is placed against the sam¬ 
ple and a pump which draws air through a hole in 
the platen (Figure 1). To avoid marking the sam¬ 
ple surface the platen is spring-loaded to limit the 
pressure which can be applied. The air passes 
through a glass tube containing Tenax, a proprie¬ 
tary absorbent, which retains vapours emitted by 
the sample. These substances are then eluted from 
the Tenax trap using 0.3ml of ethyl acetate for 
analysis by gas chromatography (GC) or mass 
spectrometry. 

In use, the unit is switched on and reaches oper¬ 
ating temperature within 5 minutes. A previously 
blanked and conditioned Tenax tube is fitted and 
the device is kept in contact with the sample sur¬ 
face. After sampling for 2-5 minutes the Tenax 
tube is removed for laboratory examination. If the 
sample is damp a simple condenser to remove ex¬ 
cess water can be fitted (Figure 2). When exam¬ 
ining grossly contaminated samples the con¬ 
tact-heater itself becomes contaminated with ex¬ 
plosives. Cross-contamination is guarded against 
by a bake-out at 120 °C and by replacing the 
PTFE tubing linking the platen to the Tenax trap. 
As a final check, it is advisable to run blanks be¬ 
fore important examinations. Existing models of 
the contact-heater have been designed and con¬ 
structed at RARDE and commercial fabrication is 
now in progress. 



CONNECTION TO PUMP 
HANDLE 


TENAX TRAP WITH SILICONE RUBBER 
CONNECTIONS 

PTFE TUBE 


SUSPENSION ASSEMBLY FOR 
FLOATING BASE'M OF4) 


SILICONE RUBBER WASHER 


INSULATION 


DISTANCE PIECE 


ALLOY BASE WITH COLLECTING 
GROOVES AND DUCT 


PERIPHERAL SHROUD 


HEATER 


THERMOCOUPLE 


CONTROL UNIT 


HANO HELO 
HEATER UNIT 



V \ \ \ \ \ \ \ V \ V 

SAMPLE 


Figure 1 A. Block-diagram of contact heater 


Performance trials 

An indication of the performance when exam¬ 
ining residues from a gelignite explosion can be 
obtained from Figures 3 and 4. The first 


PTFE TUBE TO 
TENAX TRAP 



SILICONE RUBBER 


GLASS 


PTFE TUBE TO CONTACT 
HEATER BASE 


Figure 1. Section of contact heater 


Figure 2. Improvised condenser 


406 



































































Figure 3. GC trace of contact heater extract of paper adjacent 
to a gelignite explosion (0.2ul ex 0.2ml) 



Figure 4. GC trace of ethyl acetate extract of 15 cm 2 of paper 
adjacent to gelignite explosion (0.2ul ex 5ml) 


chromatogram shows residues recovered by using 
the contact-heater for five minutes on a piece of 
thick paper located near an explosion. The second 
GC trace shows the material recovered by an ethyl 
acetate extraction of another portion of the same 
paper. The traces are qualitatively very similar and 
include both EGDN and nitroglycerine (NG), but 
the amounts present vary because thermal re¬ 
covery favours the more volatile EGDN. 

To compare contact-heater performance with 
that of the most likely recovery technique to be 
used in practice, solvent swabbing, a piece of 
plasticised upholstery PVC 0.5mm thick was ex¬ 
posed to EGDN vapour and was examined after 
36h in open air. Swabbing was performed by 
wetting 25mg of cotton wool with diethyl ether, 
shaking it once and applying the swab to 25cm 2 of 
the PVC, making three passes over the surface. 
The swab was then eluted with 1.5ml of ethyl ace¬ 
tate. Analysis of this extract failed to detect 
EGDN. A second 25cm 2 area was swabbed succes¬ 
sively with 25 swabs, and these were analysed in 
batches of five, the extracts being concentrated to 
0.3ml before GC analysis. Swabs 1-5 yielded a 


small peak corresponding to approximately 70pg 
of EGDN per injection, but analysis of the other 
swabs showed that this represented only a small 
portion of the EGDN present on the PVC; even 
swabs 20-25 contained an amount of EGDN com¬ 
parable to the amount in swabs 1-5. Using the 
contact-heater on the same PVC gave vastly im¬ 
proved sensitivity to EGDN (Figure 5), indicating 
that the technique is one to two orders of magni¬ 
tude more sensitive than single ether swabbing. 

The efficiency of contact-heater recovery of 
EGDN was quantified by placing gelignite 
cartridges in a saloon car to contaminate it, and 
then using the device to examine the various inte¬ 
rior furnishings for EGDN over a period of three 
weeks. For reference purposes the total EGDN in 
carpeting, seat PVC etc was determined by heating 
5cm 2 of sample for 2h at 100°C using the ap¬ 
paratus shown in Figure 6. Nitrogen (25ml min -1 ) 
was passed through a heated tube containing the 
sample in order to carry desorbed EGDN into a 
second tube containing toluene. In earlier experi¬ 
ments we have found that this technique recovers 
80% of EGDN present in upholstery materials. 
The results showed that virtually all exposed sur¬ 
faces had taken up EGDN vapour from the car at¬ 
mosphere, the amounts present being of the order 
of lOng cm -2 . After removal of the explosive the 
concentrations of sorbed EGDN diminished ac¬ 
cording to first order kinetics; a typical set of re¬ 
sults is shown as a semi-log graph in Figure 7. 
These results provided a yardstick for con¬ 
tact-heater recovery of EGDN and permitted the 
percentage recovery of EGDN from different sur¬ 
faces to be calculated. Table 1 shows that the re¬ 
covery with 5 minutes sampling time was typically 
8% of the amount of EGDN present. There is only 
slight evidence that this efficiency diminished as 
the interval between exposure and analysis grew 



25cm 2 swabbed 
once 

(0 5jjI exl 4ml) 



25cm 2 swabbed 
five times 
(0 5 jjI ex 0 - 3 rn I) 




100pg EGDN 


79cm J sampled for 5min 
using contact heater 
(0 5u I ex 0 2ml) 


Figure 5. GC traces of EGDN recovered from contaminated 
0.5mm thick PVC 




407 






























Figure 6. Apparatus for thermal recovery of volatile traces 



Figure 7. EGDN persistence in seat P VC 


longer. The lowest total concentration of EGDN 
found on any surface was 5ng cm and this was 
easily detected with the contact-heater. 


Table 1. RECOVERY OF EGDN FROM PVC AND CAR¬ 
PET USING THE CONTACT-HEATER 


Hours since 

exposure 

% recovery from 
door PVC carpet 

40 

17 

5 

100 

7 

— 

200 

8 

— 

350 

8 

5 

500 

— 

9 

700 

9 

8 


This comparatively high recovery, combined 
with the small volume in which recovered explo¬ 


sives is made available for analysis accounts for 
the very high sensitivity of the technique when 
compared to swabbing. 

Performance in practice 

The contact-heater has been used in connection 
with a number of vehicles involved in explosions. 
EGDN traces were found in all exposed surfaces in 
cases where the use of gelignite was suspected. The 
site of one explosion thought to have involved 
TNT was also examined, but no significant traces 
were found. Exposure to explosives in the absence 
of any explosion has also been demonstrated using 
the contact-heater. In one instance an item of 
luggage recovered after submersion in water was 
found to be grossly contaminated and EGDN, NG 
and dinitrotoluenes were recovered and identified, 
showing that it had contained gelignite. In another 
case a motor car was shown to be contaminated 
with EGDN, thus linking it with explosives, even 
though conventional chemical examination using 
swabbing and a vapour detector yielded no evi¬ 
dence of explosives. 

CONCLUSION 

A very wide range of materials may be involved 
in explosives cases, and the contact-heater re¬ 
covery technique can only assist with identifica¬ 
tion of those which are volatile. However, the 
speed, convenience and sensitivity of the con¬ 
tact-heater, combined with the frequent usage of 
explosives containing volatile constituents make it 
an attractive additional tool for the forensic 
analyst. 

ACKNOWLEDGEMENTS 

We are grateful to Dr T S Hayes and Dr E J 
Matthias for details of some forensic examina¬ 
tions. 

Copyright © Controller, Her Majesty’s Sta¬ 
tionery Office London 1983. 

REFERENCES 

1. Douse J M\ J Chromatograph 234, 415-425 
(1982). 

2. Chrostowski J E, Holmes F N, Rehn B W: 
J Forensic Sciences 21 (3), 611-15 (1976). 


408 




















THE INSTANTANEOUS DETECTION OF EXPLOSIVES 
BY TANDEM MASS SPECTROMETRY 


Scott D. Tanner, William R. Davidson and John E. Fulford 

SCIEX® 

55 Glen Cameron Road, Unit #202 
Thornhill, Ontario, L3T 1P2 
Canada 


ABSTRACT. The TAGA 6000 Tandem Mass Spectrometer (MS/MS) coupled 
with an atmospheric pressure chemical ionization (APCI) source provides a 
non-invasive method of detecting vapors from explosives in a variety of scenarios. 
The APCI source, fitted with appropriate sampling lines, allows instantaneous de¬ 
tection of these vapors in the sub-ppb (parts-per-billion) concentration ranges. 
The tandem mass spectrometer portion of the instrument provides a highly specific 
analysis of the vapors which are detected. The first mass analyzer of the MS/MS 
system is used as a separator which separates the ions formed from the various 
components of the sampled air according to their molecular weight. These ions are 
fragmented in a collision region, and the second mass analyzers used to determine 
which fragment ions are formed. The fragment ion spectrum of a compound is a 
“fingerprint” of that component which can be used for the identification of the 
component from a spectral library. Applications of the APCI/MS/MS technique 
to the detection of several explosives will be presented. Nitroglycerine, in the form 
of dynamite and double-base propellants, has been detected on aircraft, on the 
human body, in sealed cardboard boxes, in a mocked-up cargo container and on a 
cleaned revolver. Involatile explosives such as C4 can be detected from the vapors 
given off by solvents (cyclohexanone) or impurities. Remote sampling for relative¬ 
ly involatile explosives or for particles from explosives is accomplished using a 
hand-held probe concentrator which traps the vapors or particles on an organic 
coating. The sampling probe may be sealed and returned to the TAGA MS/MS 
system for analysis. Customized computer software allows for near “black-box” 
operation of the system for non-technical operators. Descriptions of the instru¬ 
ment, sampling techniques, software and applications related to explosive detec¬ 
tion will be presented. 


INTRODUCTION 

The two primary characteristics required of any 
viable explosives vapors detector are sensitivity 
and specificity. State-of-the-art detectors are ca¬ 
pable of responding to parts-per-trillion concen¬ 
tration of explosive vapors; this must be regarded 
as a minimum requirement in view of the excep¬ 
tionally low vapor pressures of the plastic and 
water-gel explosives. It is clear that when working 
at such low levels the detector must also show ex¬ 
ceptional specificity in order to prevent an unac¬ 
ceptable level of false alarms. In most practical 


applications the detector must also demonstrate a 
fast response time. 

SCIEX has been involved since its inception in 
the instantaneous detection of ultra-trace concen¬ 
trations of vapors. The approach we have taken 
has utilized Atmospheric Pressure Chemical Ioni¬ 
zation (APCI) with quadrupole mass spectrometer 
analysis and detection. APCI provides for ppt de¬ 
tectability and moderate specificity of ionization. 
Since the air sample is drawn directly into the ion 
source at approximately 1.5 liters/second, the de¬ 
tector shows essentially instantaneous response. 


409 


The mass spectrometer provides the specificity of 
molecular weight information. It should be noted 
that the sensitivity of the system can be enhanced 
by pre-concentrating the sample, for example on a 
coated adsorber wire or tenax trap followed by 
flash desorption into the ion source. 

One of the most significant recent advances in 
mass spectrometry is the development of the 
tandem mass spectrometry technique. In the 
SCIEX approach, three quadrupoles are inter¬ 
faced on axis, communicating with the APCI ion 
source at one end and the electron multiplier de¬ 
tector on the other. After ionization, the sample 
ion matrix is extracted through the atmos¬ 
phere-vacuum interface and focussed into the first 
quadrupole analyzer. Ions of a particular 
mass/charge ratio, the “parent” ions, are filtered 
from the matrix and injected directly into the 
second quadrupole region. The second quad¬ 
rupole acts as a confinement cell in which the par¬ 
ent ions are caused to collide with a molecular 
beam of neutral argon atoms. The parent ions 
thereby undergo Collision Induced Dissociation 
(CID), yielding “daughter” ions which are frag¬ 
ment ions characteristic of the structure of the 
parent ions. The daughter ions are transmitted 
into the third quadrupole region where they 
undergo mass analysis, giving rise to a characteris¬ 
tic daughter ion spectrum. The analytical scheme 
is shown in Figure 1. It should be clear that, in 
general, the MS/MS analysis provides a much 
higher specificity of analysis than a single MS. 


EXPERIMENTAL 

Most of the data presented here were obtained 
using the commercial TAGA 6000 tandem mass 
spectrometer system with APCI source. Explosive 
samples (which, regretably, were several years old) 
were cut or disturbed to expose a fresh surface. 
The samples were placed in a vial, and the vial in¬ 
serted in a glass “T” over which approximately 
1.5 1/second of room air was drawn. The entire 
air sample was introduced directly to the ion 
source through a 30 cm. glass sample line. No at¬ 
tempt was made to heat-trace the sample line, and 
no attempt at quantitation was made. 

The ambient air sample serves as the reagent gas 
for the ion source. In some instances chloroform 
was added at the ppm level to generate chloride re¬ 
agent anions. 

Single MS experiments were performed by oper¬ 
ating the second and third quadrupoles in the 
rf-only mode; mass analysis was performed only 
in the first quadrupole. MS/MS results were ob¬ 
tained by mass-analyzing in both the first and 
third quadrupoles. 

The TAGA 6000 operates in either the positive 
ion mode or negative ion mode by the application 
of appropriate focussing potentials in the source, 
analyzer and detector regions. 

RESULTS 

Previous work (Buckley et al. (1978)) has shown 
that nitroglycerine (NG), ethylene glycol dinitrate 


INLET 



SOURCE 


COLLISION DATA SYSTEM 

REGION 








COMPLEX 


HIGHLY SPECIFIC 

MIXTURE 


IONIZATION 


SEPARATION 
ACCORDING 
TO MASS 


FRAGMENTATION 


— 

SEPARATION OF 
FRAGMENTS 


FRAGMENT 

SPECTRUM 


APCI /MS /MS 


Figure 1. Schematic of analysis of ambient air by APCI/MS/MS. 


410 































4000000 


(S) 

Q. 

O 


GO 

z 

UJ 


3000000 - 


2000000 - 


1000000 - 


La 


NO, 


PISTOL POWDER 


single MS / negative mode 


181 


0—|- I I*-! “|-1“ I 

10 50 


- i ■ I 


225 


287 


—A 


100 


150 


200 


■p —I i ‘ t 

250 300 


MASS/CHARGE 

Figure 2. Single MS spectrum (negative mode) of the headspace volatiles above double-base pistol powder. 


(EGDN), dinitroluene (DNT) and trinitrotoluene 
(TNT) are most sensitively detected in the negative 
ion mode. An additional advantage of this is that, 
in general, less interference is observed in the 
negative mode due to the higher specificity of 
negative ionization under APCI. The single MS 
(negative mode) spectrum of the volatiles emanat¬ 
ing from double-base pistol powder is given in 
Figure 2. 

The most prominant responses are observed at 
m/z = 62, 181, 225 and 287. A smaller response at 
m/z = 227, corresponding to the molecular ion 
(M-) of the NG is observed. The large response 
at m/z = 62, corresponding to N03 - , is a typical 
fragment ion of organonitrate compounds 
(notably EGDN), but is considered not to be spe¬ 
cific enough to trigger an alarm for explosives. 
The CID spectra of the remaining ions were re¬ 
corded in order to assist in the identification of 
these vapors, and are given in Figure 3. 

Both the parents at m/z= 181 and 225 give rise 
to predominant N03 - with a less intense N02- 
peak. As such, one can conclude that each corre¬ 
sponds to an organonitrate species; they may be 
assigned to NG, assuming the loss of N02 and H2 
in the ionization process, respectively. On the 
other hand, the m/z = 287 parent ion yields essen¬ 


tially only the C03 - daughter ion at m/z = 60; 
the m/z = 287 parent ion clearly corresponds to 
the cluster ion (NG.C03)- formed as a primary 
product in the ion source. The observation of this 
cluster ion leads one to conclude that the most 
sensitive approach to the detection of NG might 
be to induce such a clustering reaction. Chloro¬ 
form was added to the ambient air sample to gen¬ 
eral reagent Cl- ions. The single MS spectrum 
observed under these conditions is shown in Fig¬ 
ure 4. Strong responses at the m/z = 262 and 264 
ions, in approximately the expected 3:1 ratio, are 
obtained. The CID spectra for these parent ions, 
given in Figure 5, show approximately equivalent 
responses for the daughter ions Cl -, N02- and 
N03 -. The relatively strong responses for the 
N02- and N03 - daughter ions are somewhat 
surprising, and suggest that the (NG.C1) - adduct 
bond has a strong covalent nature comparable to 
the strength of the C-O and N-O bonds of the 
nitrate functional group. It should also be noted 
that the formation of the Cl adduct of NG re¬ 
moves the MS response to a higher mass region 
where chemical interference will be less important; 
this could be emphasized by using bromoform as 
the chemical ionization reagent. 

A number of volatiles were observed in the 


411 







S 1OB000- 



PISTOL POWDER 


CID on m/z“181(-) 


NO " 


3 

- N0 2 " 

..L. , | 




MASS/CHARGE 


MASS/CHARGE 


Figure 4. Single MS spectrum of the headspace volatiles above 
doublebase pistol powder using Cl - chemical ionization. 




MASS/CHARGE 

Figure 3. C1D spectra of some of the parent ions observed 
upon ionization of the headspace vapors above double-base 
pistol powder. 

headspace vapors above a sample of recrystallized 
TNT, as shown in Figure 6. The CID spectra of 
the m/z = 197, 226 and 227 ions are given in Figure 
7. All show a prominant N02- daughter ion. It 
can be concluded that the m/z = 227 ion corre¬ 
sponds to M - , m/z = 226 to (M - 1) - (loss of a 
proton) and m/z =197 to (M-NO)- (probably 
due to nucleophilic substitution of reagent O - for 
N02). 


The headspace above RDX was examined under 
positive ionization. Several volatiles were ob¬ 
served (Figure 8), some of which may be useful for 
the detection of RDX. Of particular interest was 
the ion appearing at m/z = 223, which corresponds 
to the molecular weight of protonated RDX. In 
view of the extremely low volatility of RDX, it 
would be surprising to see this ion. This suspicion 
was confirmed by running the CID spectrum of 
the m/z = 223 ion, which identified that ion as 
protonated diethylphthalate (a common plasti¬ 
cizer). This result emphasizes that false alarms 
may be triggered even given the specificity of mass 
spectrometry, but such false alarms can be avoid¬ 
ed by using the enhanced specificity of MS/MS. 

The TAGA system has been specifically de¬ 
signed for immediate (real-time) response to 
changes in the concentrations of trace vapors in 
ambient air. Figure 9 shows the real-time response 
(single MS mode) to samples of TNT, DNT and 
NG momentarily introduced near the inlet of the 
TAGA. The real-time MS/MS response to TNT, 
monitoring the formation of the N02- daughter 
ion from the m/z = 227 and 197 parent ions, is 
shown in Figure 10. As no attempt was made to 
heat-trace the sample inlet, some sample line 
memory is observed as a long “tail” after the sam¬ 
ple was removed; in a real-life situation the sam¬ 
ple line would be heated to eliminate this memory 
effect. 

CONCLUSION 

The TAGA MS/MS system with Atmospheric 
Pressure Chemical Ionization permits the instan¬ 
taneous detection of trace concentrations of ex¬ 
plosives vapors in air. All of the explosives studied 
gave rise to a number of volatiles, some of which 
may be useful for the detection of explosives; 


412 





























ION INTENSITY (CPS) 


6000a 


uo 

Q_ 

O 


50000 - 


40000 - 


35 - 
Cl 


NO, 


NO, 


PISTOL POWDER 

CID on m/z=262(-) 
Ionization by Cl attachment 


>- 
i— 
>—» 
oo 


30000 - 


20000 - 


10000 - 


0-1- 1 I ■- -'- 1 **■ — I -'-1-'-1- T - 1 - 1 - 1 -'- 1 -'- 1 -'- 1 -'- 1 - 

10 40 60 80 100 120 140 160 180 200 220 240 270 


MASS/CHARGE 



MASS/CHARGE 


Figure 5. CID spectra of the chloride-adduct ions of NG. 


413 















Figure 6. Single MS spectrum (negative mode) of the headspace volatiles above TNT. 


more effort on the characterization of these con¬ 
comitant vapors is warranted. Nitroglycerine is 
most sensitively detected in the negative ionization 
mode using Cl - as the reagent ion to promote the 
formation of the halide-NG adduct ion. TNT may 
be detected readily as the M - ion and as the 
M-NO)- ion. Collision Induced Dissociation of 
the nitrate-explosives (NG, EGDN) gives rise to 
prominent N03 - daughter ions, while the 
nitro-explosives (TNT, DNT) generate N02- 
daughter ions. Caution is advised in the analysis 
of single MS results: the detection of diethylph- 
thalate of m/z = 223 could be confused with RDX 


(which is isobaric, i.e. has the same nominal mo¬ 
lecular weight), although MS/MS can readily dis¬ 
tinguish the two. 

REFERENCES 

Buckley J. A., French, J. B. and Reid, N. M. 
(1978). TAGA, a total system approach to 
sub-ppt explosive detection by natural vapor 
identification. Proceedings of the New Con¬ 
cepts Symposium and Workshop on Detection 
and Identification of Explosives, Reston, Vir¬ 
ginia, P109. 


414 





















































ION INTENSITY (CPS) I0N INTENSITY(CPS) 10N INTENSITY (CPS) 


10O000 


90000 - 

60000 - 

70000 - 

60000 - 

50000 - 

40000 - 

30000 - 

20000 - 

10000 - 

0 


NO- 


77 


I 1 ' l 1 . . - 4 1, 


TNT 

CID on ra/z=197(-) 


120 


10 20 


40 


60 


68 


100 120 


140 


160 


180 200 


MASS/CHARGE 



MASS/CHARGE 


Figure 7. CID spectra of some of the parent ions observed upon ionization of the headspace vapors above TNT. 


415 



















ION INTENSITY (CPS) I0N INTENSITY (CPS) 



REAL-TIME DETECTION OF TNT, DNT AND NG (by single MS) 



TIME (SECONDS) 

Figure 9. Real-time response (single MS) to TNT, DNT and NG. 


416 












































ION INTENSITY (CPS) 



TIME (SECONDS) 

Figure 10. Real-time response to TNT by MS/MS. 


417 

























































A MAN PORTABLE GCMS FOR EXPLOSIVES DETECTION 


Dr. Russell C. Drew 
American Innovation, Inc. 

701 Clear Spring Road 
Great Falls, Virginia 22066 

and 

Dr. Christopher M. Stevens 
California Institute of Technology 
Jet Propulsion Laboratory 
Pasadena, California 91109 


ABSTRACT. A highly integrated design, light-weight and low power consump¬ 
tion gas chromatograph-mass spectrometer has been developed and successfully 
operated as part of the NASA Viking mission to the surface of Mars. 1 The rigorous 
criteria established by NASA for the Viking Mars Lander resulted in an instrument 
that was physically compact, highly shock resistant and capable of remote opera¬ 
tion through a command and control linkage with data return to earth. The design 
of this instrument evolved over an eight year period of extensive analytical testing 
and refinement of system elements to meet the specifications established for re¬ 
mote planetary operations. The principal elements of the Viking GCMS are being 
re-packaged into a configuration suitable for terrestrial analytical applications 
ranging from environmental monitoring to a variety of forensic and security uses, 
including explosives detection. The result is a unique analytical tool that combines 
the power and sensitivity of a laboratory GCMS instrument in a small valise-sized, 
man-portable device that will allow field measurements and identification of un¬ 
known volatiles with maximum sensitivities of the order of 0.1 parts per billion (in 
air by volume). The essential design and operational characteristics of the Viking 
GCMS system will be highlighted in connection with explosives detection applica¬ 
tions. 


INTRODUCTION 

The combination of Gas Chromatography with 
Mass Spectrometry over 25 years ago 2 brought to¬ 
gether these two powerful analytical tools to pro¬ 
vide a new capability for organic analyses that has 
been applied to an increasingly diverse series of 
applications. The technique is perhaps most effec¬ 
tive when complex organic mixtures are involved 
as well as with samples that are very dilute and 
quite often in the presence of contaminants or oth¬ 
er masking compounds. Such conditions often 
confront the forensic scientist, with the result that 
numerous examples of GCMS use in this field 
have been reported. 3 A particularly important use 
is in analysis of explosives and high energy propel¬ 
lants, which has been discussed in a recent survey 


of the field by Yinon and Zitrin (Pergamon Press, 
1981). Mass spectra of explosives and explosive 
mixtures have been catalogued and variations in 
their characteristics under various forms of ioniza¬ 
tion schemes have also been investigated. 4 

For the most part, commercial GCMS systems 
have been intended for laboratory use, in which 
there is a highly controlled environment with little 
effective limitation on space or power require¬ 
ments for the instrument. There are a variety of 
such systems commercially available, with very 
high sensitivity and recently, with mass ranges that 
are well above 1,000 amu. These units typically are 
designed to be flexible and permit different ioniza¬ 
tion approaches and sample handling techniques 
and frequently are teamed with a microprocessor 


419 


for automatic adjustment of electric potentials 
and other controllable variables. Sophisticated 
data handling and processing is provided with li¬ 
brary search and signature recognition capability 
becoming available. A major improvement in 
computer-aided interpretation of unknown spec¬ 
tra using the probability-based matching (PBM) 
system has recently been reported 5 that will permit 
real-time, on-line identifications to be made dur¬ 
ing the GCMS run. Further improvements seem 
likely and alternative approaches to comput¬ 
er-aided compound identification are being pur¬ 
sued that have similar capabilities. In short, the 
techniques of GCMS analysis have been refined 
and are continuing to improve to provide even 
greater efficiency and versatility for a wide range 
of organic analyses. 

While the laboratory use of GCMS has flou¬ 
rished, the development of field portable instru¬ 
ments with these capabilities has been very lim¬ 
ited. One approach, taken by a Canadian Firm, 
SCIEX, Inc., involved essentially moving a labo¬ 
ratory instrument, with some modifications into a 
large, mobile van. 6 This system, using the TAGA 
3000 GCMS instrument, with atmospheric pres¬ 
sure chemical ionization, has been used for a vari¬ 
ety of field environmental measurements where 
the Van and GCMS could be brought to the vicin¬ 
ity of the test site. Another approach that has been 
taken has been to miniaturize and ruggedize just 
the MS portion of the system, to produce a port¬ 
able mass-analyzer that can be taken into the field 
with relative case. 

This paper will describe the development of a 
complete, man-portable GCMS, of high sensitiv¬ 
ity, with simplified operational characteristics and 
proven performance. 

THE VIKING GCMS 

In the early 1970’s, the National Aeronautics 
and Space Administration was given approval for 
a series of two unmanned scientific missions to 
Mars, to orbit the planet at close range and to 
place two landers on the surface to perform scien¬ 
tific measurements including tests for the presence 
of life or complex organic substances that may be 
a precursor to life. The challenge facing NASA 
was to condense a carefully chosen set of instru¬ 
ments that would perform the required tests into a 
very compact and light-weight lander system cap¬ 
able of withstanding the rigors of heat-soak ster¬ 
ilization, launch vibrations and accelerations, then 
traverse interplanetary space for six months or so, 


and after the shock of landing on Mars, function 
successfully millions of miles from earth, subject 
to cold surface temperatures and blowing dust. 

A key instrument in the experiment package was 
a GCMS because of its flexibility and specificity in 
identifying unknown substances as well as its sen¬ 
sitivity. The development of the Viking GCMS 
was carried out at the Jet Propulsion Laboratory 
of the California Institute of Technology, sup¬ 
ported by several major contractors and the Vik¬ 
ing science team. A detailed description of the de¬ 
velopment of this instrument has been published 8 
and the scientific results from its successful opera¬ 
tion on the surface of Mars have been reported. 9-14 
The current development of a terrestrial, 
man-portable GCMS is largely based upon the 
Viking instrument, the essential features of which 
will be summarized here. 

The Viking GCMS can best be understood 
through reference to a systematic flow diagram, 
Figure 1. The instrument was designed to permit 
direct atmospheric sampling through a molecular 
leak, Valve 9 then Valve 12, for test of atmospher¬ 
ic constituents, after removal of carbon mon¬ 
oxide, carbon dioxide and water. For full GCMS 
testing, soil samples were collected, introduced in¬ 
to the sample processor, were pyrolyzed and the 
vapors were eluted with hydrogen as a carrier gas 
and introduced to the GC column. Downstream of 
the column is a five-stage effluent splitter (Valves 
4, 4A, 5, 6, and Restrictors R5, 6, 7) which is con¬ 
trolled by the MS ion pump to prevent pump over¬ 
load and maintain sample concentrations within 
the analyzing range of the MS. A palladium alloy 
separator is used to remove the hydrogen carrier 
gas, and the sample is introduced into the MS 
through V7. 

The MS is a Nier-Johnson, 90° electric sector, 
90° magnetic sector double-focussing instrument, 
electrically scanned, with a mass range of 12-215 
amu. It uses an electron bombardment ion source 
with selectable ionizing energies of 45 and 70 eV, 
and a relatively slow scan rate of 10 sec. The ion 
pump for the MS uses the same magnet as the 
magnetic sector, with pumping speed for most 
gases of 500 cm 3 /sec. This design approach al¬ 
lowed a very compact MS assembly and kept in¬ 
strument weight down. 

The GC is a micropacked column, 2m long by 
0.75mm I.D., packed with Tenax-GC, 60-80 
mesh coated with 2 percent solution of Poly- 
MPE. The demonstrated performance of the Vik¬ 
ing GCMS included a resolution of 200 (10 percent 


420 



~1 = PARTS OF SYSTEM ACTIVATED 
DURING PHASE 1 

ft. 1 = PARTS OF NO RELEVANCE TO 
THIS TASK 


Figure 1. Viking GCMS flow diagram. 


valley) at 200 amu with a detector sensitivity of 1.7 
x 10“ 8 amps/ngm-sec. Figure 2 is a block diagram 
of the major subsystems and their relationships. 

An important part of the design criteria for the 
Viking GCMS was to minimize both the weight 
and volume of the unit and reduce power require¬ 
ments in order to reduce demands upon the Lan¬ 
der which was highly weight and power con- 
trained. Another important characteristic is the re¬ 
sistance to shock and vibration that was required 
in order to space-qualify the instrument. Addi¬ 
tionally, there was an obvious requirement for re¬ 
mote-control operation of the system which en¬ 
tailed special attention to interfaces, stability of 
operation, pre-programmed functions and se¬ 
quencing, electrically operated precision valves, 
and a highly reliable data collection and relay sys¬ 
tem. All of these aspects of the Viking GCMS de¬ 
sign make it particularly suitable for adaptation to 
a portable terrestrial instrument. 

Terrestrial Adaptation 

After the Viking Mars landing mission, there 
were two spare flight instruments that have been 



Figure 2. Flight configuration of the Viking GCMS. 

kept under vacuum in a standby mode for six 
years. One of these instruments is being modified 
to establish the feasibility of a portable terrestrial 
GCMS system, suitable for a variety of in situ ana¬ 
lytical applications. 


421 

















































































The principal subsystems that require modifica¬ 
tion from the original Viking configuration are the 
GC column, the GC-MS interface and the scan 
rate and mass range of the MS. In addition, suit¬ 
able methods of sample collection and introduc¬ 
tion into the GCMS must be defined, depending 
upon the nature of the application. 

Specific design criteria for these subsystems are 
reviewed in the following sections. 

Mass Spectrometer 

The MS in the Viking instrument has a mass 
range of 12-215 amu. However, for most portable 
terrestrial applications a range of about 400 amu 
will be necessary to make adequate identification 
of many of the complex spectra that will be en¬ 
countered. In the MS, the following relationship 
connects the Mass and the two major variables 
(magnetic field and ion accelerating voltage): 

M = 4.8 x 10“ 5 (RB) - 

V 

where R = radius of curvature of the magnetic 
sector (cm) 

B = magnetic flux density (gauss) 

M = mass of the ion (amu) 

In the existing instrument, R = 3.8cm, B = 
6330 gauss, and V varies between 130 and 2330 
volts. To focus higher masses on the detector, 
either the accelerating voltage or the magnetic 
field must be changed. If the accelerating voltage 
is lowered, however, the result will be an increase 
in velocity aberration and consequent loss of reso¬ 
lution as well as loss of sensitivity because of the 
greater number of ions that drift off the instru¬ 
ment axis. The alternate approach has been 
chosen, that is, an increase in magnetic flux densi¬ 
ty to 9000 gauss, which results in an accelerating 
voltage of 140 for mass 400. The velocity aberra¬ 
tion will cause a slight decrease in resolution of the 
MS at the higher mass numbers. The scan time of 
the MS will be decreased from 10 sec. to 3 sec. to 
improve sample analysis. 

Interface Between the GC and MS 

The Palladium-silver separator will be replaced 
by a two-stage membrane separator in order to 
avoid possible chemical reaction with the carrier 
gas, hydrogen, with palladium acting as the cata¬ 
lyst. This interaction would seriously affect PCB 
detections, for applications. The new interface 
will be connected to the GC column and will be 
heated simultaneously within the thermal zone to 


eliminate the need for a separate heater. A silicone 
membrane is being investigated together with a 
simple cannister pump of sorptive material in the 
interstage region of the separator to aid in remov¬ 
ing the carrier gas. 

Gas Chromatograph Column 

A modern fused silica WCOT capillary GC col¬ 
umn will replace the original Viking GC packed 
micro column. In order to shorten analysis time, 
which is especially important to a field portable in¬ 
strument, the GC typically will operate in a man¬ 
ner that provides only sufficient separation to al¬ 
low unambiguous identification and quantitation 
of samples by the MS while maintaining total 
analysis time within reasonable limits. 

For many terrestrial applications, the effluent 
from the capillary GC column will be split, with 
one part sent to an electron capture detector 
(ECD) and one part to the MS through the separa¬ 
tor membranes. The ECD will assist in monitoring 
the performance of the GC column. 

Auxiliary Subsystems 

Sample introduction into the GCMS requires 
both a detailed understanding of the likely field 
environments to be encountered and the charac¬ 
teristics of the substances that are to be identified. 
Collection of vapor samples, if sample concentra¬ 
tions are high, may be made with a simple probe 
or, if relatively simple mixtures are present, via di¬ 
rect injection into the MS through a molecular 
leak. Most applications, however, require further 
sample processing before introduction into the GC 
or MS. In general, the sample collection subsys¬ 
tem will have a probe with a small pump to obtain 
adequate flow into the concentrator cartridge 
which will be thermally desorbed and directed 
either to the GC or directly to the MS depending 
upon the nature of the application being carried 
out. Other examples of the sample pre-processing 
are beyond the scope of this paper. A survey of 
typical methods for various explosives analyses 
may be found in the recent monograph by Yinon 
and Zitrin. 15 

A particularly important part of any modern 
GCMS is the data processing, storage, retrieval, 
and analysis subsystem. The Viking GCMS in its 
basic design is compatible with a high degree of 
automation and computer-aided data handling. 
Valve sequencing and operation of the system will 
be computer controlled as well as initial data han¬ 
dling. The resolved ion current analogue signal 


422 



(RIC) from the MS detector will be digitized and 
processed using a data processing system devel¬ 
oped at JPL under the sponsorship of the Nation¬ 
al Institute of Health. 16 The fully portable system 
will include an on-board microprocessor system, 
capable of supporting fully automatic systems 
operation. Investigation of on-board signature 
analysis capability is in process, to complement 
the operating system control functions. 

EXPERIMENTAL PROGRAM 


generation system which is a direct extrapolation 
of the Viking Mars Lander instrument as well as 
subsequent incremental improvements currently 
planned. 

Power 

The power requirements for the proposed 
GCMS are not significantly different from the 
Mars Lander GCMS power requirements. A com¬ 
plete GCMS analysis on the Viking instrument 
lasting one hour would consume power at the rate 
of 80 watts. The instrument would therefore re- 


With these general directions established, the 
process of concept validation has been underway 
at the Jet Propulsion Laboratory, with a special 
emphasis upon the capability to test for organic 
vapors, such as PCBs or explosives. The perfor¬ 
mance objectives of this program are outlined in 
Table 1. This shows the specifications for a first 

quire 80 watt-hour of energy per analysis. The 
necessary power could be tapped from a domestic 
power line or from an internal power supply. In 
any event, a small battery would be required to 
maintain operation of the ion pumps which will 
consume 0.04 watts in the instrument standby 
mode. 

Table 1 

“First Generation” 

Viking GCMS 
(System One) 

Viking GCMS w/ 
Generic Magnetic 

Sector 

Viking GCMS 
w/EOlD 

Mass Range 

a) 12-215 amu 

b) 24-430 amu 

12-500 amu 

Two ranges 

12-78 amu 

78-507 amu 

Scan Rate 

3 sec over 

mass range 

3 seconds 

Non scanning 
> 40 ms/range spec¬ 
tral integration time 

Ionization Mode 

El 

25 eV and 75 eV 

El 

10-100 eV or 

Field Ionization 

El 

10-100 eV or 

Field Ionization 

Resolution 

200 @ 200-400 amu 

10% valley 
(entire mass range) 

500 @ 500 amu 

10% valley 

500 @ 500 amu 

10% valley 

Size/Weight 

21 Kg + battery 
weight * 

TDB—This would 

determine ultimate 
specifications 

25-30 Kg + 
battery weight * 

Operating Mode 

GCMS 

Direct MS 

Enriched MS 

GCMS 

Direct MS 

Enriched MS 

GCMS 

Direct MS 

Enriched MS 

Mass Stability 

± 0.1 amu 

± 0.1 amu 

± 0.1 amu 

Detector Sensitivity 

2.5 x 10~ 8 A/ng/sec 
10-13A-10-6A 
dynamic range 

2.5 x 10~ 8 A/ng/sec 
10-DA-10-6A 
dynamic range 

10- >5 gm detectability 


* 0.9 Kg per hour of operation 


423 












Figure 3. Laboratory test configuration of the mass spectrom¬ 
eter. 

It is estimated that an on-board power supply 
(battery pack) would weigh approximately 0.9 kg 
per hour of operation. 

Weight of the System 

The existing Viking GCMS system weighs 18 kg 
including the electronics. Adding the necessary 
modifications such as a larger magnet, GC col¬ 
umn, an appendage ion pump, a two stage mem¬ 
brane separator with its own intermediate stage 
pump, electronics, interface box, a sample extrac¬ 
tion kit and an aluminum carrying case would in¬ 
crease the weight to about 27 to 29 kg. 

Figure 3 shows the flow diagram of the mass an¬ 
alyzer, modified for validation testing. Using a 
modified Mars flight instrument shown in Figure 
4, that had been quiescent for over six years, two 
test compounds were introduced into the MS sys¬ 
tem to demonstrate system operation, sensitivity 
and mass resolving power. To provide insurance 
that an adequate vacuum was maintained an auxil¬ 
iary laboratory system was connected to the MS 
since control circuitry for RIC was not connected. 
This later proved to be redundant. 

The two compounds chosen to illustrate MS 
operation were Octafluorocyclobutane (C 4 F 8 ) 
(molecular weight = 200 amu) and Octafluorobu- 
tene-2 (C 4 F 8 ) (molecular weight = 200). These 
two test samples were chosen because the ion frag¬ 
ments generated from electron impact ionization 
cover the full mass range of the instrument for one 
of them, and nearly the full mass range for the 
other. 

The mass spectrum of octafluorocyclobutane 
(C 4 F 8 ) is shown in Figure 5A. The mass spectrum 
was as expected. The parent molecule is unstable 


and the most intense fragment ion appears at 
C 3 FG or m/e = 131. Very little ion intensity 
should be seen at the parent mass (m/e = 200), as 
was observed. The strong ion signals at masses 
100, 69, and 31 were produced by the fragment 
ions C 2 FG, CFG, and CF + , respectively. Some 
doubly charged ion peaks were observed, as ex¬ 
pected. 

Octafluorobutene-2, on the other hand, is a 
more stable molecule. Hence a strong molecular 
ion at m/e = 200 was observed (See Figure 5B). 
The expected two most prominent peaks in the 
spectrum, m/e = 69 (CFG) and m/e - 131 
(C 3 F 5 + ) were seen as was (M - F) + at m/e = 181. 
Doubly charged ions were also observed from this 
sample. 

The sensitivities determined from these meas¬ 
urements are 0.8 x 10 s A-ng^'-s" 1 at the 131 
amu base peak for octafluorobutene-2 and 2.3 x 
10 s A - ng' 1 - s'' at the 100 amu base peak for 
octafluorocyclobutane. This is consistent with and 
comparable to the Viking design sensitivity of 1.7 
x10 s A - ng" 1 - s' 1 at 28 amu for nitrogen. 

Mass resolving power measured at m/e = 100 
and 181 is approximately 180 by the 10 percent 
valley definition commonly used in organic mass 
spectrometry. This is slightly below the design 
value of 200 but was expected from the higher in¬ 
strument pressure. The pressure was higher than 
designed because it was operated without the in¬ 
tegral ion pump being activated. Scattering of the 
ion beams by gas in the spectrometer analyzer is 
the cause of this phenomenon. 

FUTURE WORK 

Preliminary results of the terrestrial adaptation 
of the Viking GCMS have been encouraging and 
the next steps toward a fully portable instrument 
are underway. A prototype configuration for such 
an instrument has been established and is shown in 
Figure 6. Clearly, the major hardware elements of 
the system are easily contained in a small 
brief-case sized package which also accommo¬ 
dates the supporting electronics, battery, carrier 
gas supply and sample concentrator subsystem. 
Not shown is auxiliary equipment that may be 
used in connection with the introduction of sam¬ 
ples to the GCMS. Preparation of samples is ex¬ 
pected to involve a separate kit that would differ 
in detail depending upon the specific applications 
to which the GCMS would be applied. In testing 
for explosives, for example, both a vapor inlet 
probe and pre-concentrator would be included as 


424 



















Figure 4. 


well as elements that would permit various previ¬ 
ously tested extraction techniques to be utilized. 

Other uses would require a similar sample 
pre-processing kit but with different reagents. 

Additional attention is being given to the con¬ 
trol and display subsystems, including use of a flat 
plate programmable display unit that would fit 


within the unit shown. With the successful demon¬ 
stration of a fully adapted Viking GCMS system, 
versatile and sensitive laboratory-level GCMS 
performance will become available for truly port¬ 
able analysis and field applications, which should 
be of value to a wide variety of explosives detec¬ 
tion applications. 


425 





4 

J-— * 


1 

8 OCTAFLUOROCYCLOBUTANE 

1 . 




‘ 


_ _ ■ ‘ — 


131 100 69 


181 150 

___ . i 

9 

> 

3 

! 1 

62 

1 | 

-----L-_■ 



31 28 18 

. OCTAFLUOROBUTENE-2 


50 

.1 

4 

. . .J 


. 1 . . 

1 . 

A-- 1 . ... - 





131 100 93 69 


200 181 150 


i 


t 


62 5 

J 

! 1_il 


J J J 1 


Figure 5A. Mass spectrum of octafluorocyclobutane obtained 
from the modified Viking mass spectrometer. 5B. Mass 
spectrum of octafluorobutene-2 obtained from the modified 
Viking mass spectrometer. 

REFERENCES 

1. Rushneck, Diaz, et al. “Viking Gas Chro¬ 
matograph-Mass Spectrometer”, Rev. Sci. 
Instrum., 49(6), June 1978. 

2. W. H. McFadden. Techniques of Combined 
Gas Chromatography/Mass Spectrome¬ 
try: Applications in Organic Analysis, John 
Wiley & Sons, Inc., New York, 1973. 

3. The number of such examples is very large 
and the following provides a limited sampling: 
Beveridge, A. D., S. F. Payton, R. J. Au- 
dette, A. J. Latnbertus and R. C. Shaddick, 
(1975). J. Forensic Sci. 20, 431. 

Buckley, J. A., J. B. French and N. M. Reid 
(1978). “Taga, a Total System Approach to 
Sub-ppt Explosive Detection by Natural Va¬ 
pour Identification”, Proc. of New Concepts 
Symposium and Workshop on the Detection 
and Identification of Explosives, Reston, VA, 
p. 109. 


Karasek, F. W., (1978). Industrial Research/ 
Development, December, 86. 

Mach, M. H., A. Pallos and P. F. Jones 
(1978). J. Forensic Sci. 23, 433, 446. 

Yinon J. and S. Zitrin (1977). J. Forensic Sci. 
22, 742. 

4. Examples are: 

Brown, C. L. and W. P. Weber (1970). J. 
Am. Chem. Soc. 92, 5775. 

Brunnee C., G. Kappus and K. H. Maurer 
(1967). Fres. Z. Anal. Chem. 232, 17. 

Mach, M. H., A. Pallos and P. F. Jones, 
(1978). J. Forensic Sci. 23, 433, 446. 

Schulten, H. R. (1977). “Field Desorption 
Mass Spectrometry and Its Application in 
Biochemical Analysis” in “Methods of Bio¬ 
chemical Analysis”, Vol. 24, D. Glick, Ed., 
Wiley, Inc. 

Tan, Y. L. (1977). J. Chromatogr. 140,41. 
Zitrin, S. and J. Yinon (1976). Org. Mass 
Spect. 11, 388. 

5. In Ki Mun, D. R. Bartholomew, D. B. Stauf¬ 
fer, F. W. McLafferty. “Weighted File Or¬ 
dering for Fast Matching of Mass Spectra 
Against A Comprehensive Data Base”, An¬ 
alytical Chemistry, 53, (1981). 

6. Lane, D. A., “Mobile Mass Spectrometry”, 
Environ. Sci. Technol., Vol. 16, No. 1, 1982. 

7. Evans, J. E. and J. T. Arnold (1975). Envi¬ 
ronmental Science & Technology, 9, 1134. 

8. Op. cit., Rushneck, Diaz, et al., June 1978. 

9. Owen, T. and K. Biemann, (1976). Science 
193, 80. 

10. Biemann, K., J. Oro, P. Toulmin III, et al., 
(1976). Science 194, 72. 

11. Biemann, K., T. Owen, D. .R. Rushneck, et 
al., (1976). Science 194, 76. 

12. Owen T., K. Biemann, D. R. Rushneck, 
(1976). Science 194, 1293. 

13. Biemann, K., J. Oro, P. Toulmin III, et al., 
(1977). J. Geophysical Res. 82, 4641. 

14. Owen, T., K. Biemann, D. R. Rushneck, et 
al., (1977). J. Geophysical Res. 82, 4635. 

15. Jehuda Yinon and Shmuel Zitrin, The 
Analysis of Explosives, Pergamon Press, ed. 
1981. 

16. Giffin, C. E., Britten, R. A., and Johansen, 
R. A., Proc. Mass Spectro. Allied Topics, 
New York, May 25-30, 1980. 


426 







































— 



Figure 6. 


427 



















































































TRACE VAPOR DETECTION 
OF HIDDEN EXPLOSIVES 


Lome Ei las 

National Resource Council 
of Canada 

Paper No. 49 not submitted for publication. 


429 




































SAMPLING OF EXPLOSIVES 
WITH 

MULTIPLE, PORTABLE PRECONCENTRATING CARTRIDGES 


Ralph J. Sullivan 
and 

Gary W. Watson 
XonTech, Inc. 

6862 Hayvenhurst Avenue 
Van Nuys, California 91406 


ABSTRACT. A portable personal sampler has been developed to be used in 
searches for explosives. The personal sampler draws air through a cartridge where 
explosive vapors are preferentially absorbed on a treated filament. This preferen¬ 
tial adsorption results in a preconcentration of explosive vapors. The cartridge is 
then removed and inserted into XonTech’s Model GC-710 Explosive Detector 
where the cartridge filament is heated and the flashed off vapors are detected with 
an electron capture detector. Many commercial explosives, including TNT, C-4, 
dynamite, and detasheet, have been detected. Retention and sampling time curves 
for explosives show that detection is possible up to 30 minutes after sampling. The 
sampler is small (1.5 pounds) and relatively inexpensive. Several cartridges may be 
used with one sampler and several samplers may be used with one GC-710, thereby 
reducing the investment for search equipment. 


INTRODUCTION 

XonTech, Inc. manufactures and sells the port¬ 
able Model GC-710 Explosive Detector shown in 
Figure 1. While the GC-710 has been shown to be 
very effective in the detection of explosives, many 
of our prospective customers have asked if there is 
a less expensive way to conduct a search than for 
each searcher to carry a GC-710. The answer to 
this question is the subject of this paper which de¬ 
scribes the use of the Model 7101 Personal Sam¬ 
pler. 

The XonTech Model 7101 Personal Sampler is a 
small hand-held pump which draws air through a 
removable cartridge (Figure 2). The cartridge is in¬ 
terchangeable with the cartridge in the Model 
GC-710. Thus, a sample may be taken with a car¬ 
tridge in the Personal Sampler, the cartridge re¬ 
moved, and the cartridge analyzed in the GC-710. 
The use of two to five Personal Samplers with 
three to five cartridges associated with each Per¬ 
sonal Sampler would obviously allow more people 
to search using a single GC-710. 

To evaluate the performance of the Personal 
Sampler, tests were run to determine its applicabil¬ 


ity to an actual search. The efficiency of adsorp¬ 
tion, the length of sample time, the dependence on 
flowrates, and the time between sampling and de¬ 
tection are described. 

EXPERIMENTAL 

A XonTech Model GC-710 was used for all of 
the analyses presented in the paper. The GC-710 is 
a gas chromatograph containing a 10" x '/»" O.D. 
FEP column of OV-275 on 40-60 mesh Chromo- 
sorb WAW. The oven temperature was isothermal 
and was set between 90 and 125 ° C in order to sep¬ 
arate the explosive from the air peak. The detector 
is a direct current ECD using tritium (M50 mCi). 
The carrier gas is helium at a flowrate of 250 
cc/min. Sample injection was made using a Xon¬ 
Tech patented valve and cartridge (U.S. Patent 
4,128,008). The cartridge contains a platinum fila¬ 
ment which is treated with a chromatographic sta¬ 
tionary phase (Figure 3). This chemical coating 
acts as a preconcentrator to remove the explosives 
from the air. Air is drawn over the filament at 300 
to 500 cc/min. The absorbed explosive is injected 
into the GC by pneumatically inserting the car- 


431 



Figure 1. The XonTech Model GC-710 Explosive Detector 
and Model 7101 Personal Sampler. 


tridge into the helium carrier gas stream. The ex¬ 
plosive is released when the filament is heated. 

This thermal release of explosives probably re¬ 
sults in their decomposition. The result is that a 
large number of explosives give a substance which 
elutes within 6 to 9 seconds after injection. Inde¬ 
pendent evaluations have shown that many explo¬ 
sives elute a peak during the alarm window of the 
GC-710. These data are summarized in Table 1. 

A XonTech Model 7101 Personal Sampler was 



Figure 2. XonTech Model 7101 Personal Sampler with Sam¬ 
pling Cartridge and Battery Charger. 


modified so that its pump was removed and it 
could be attached directly to the GC-710. This 
procedure allowed two cartridges to be tested in 
series. The efficiency of the upstream cartridge 
could be measured using this configuration (Fig¬ 
ure 4-5). 

The direct injection of samples into the GC-710 
was used to determine the flow dependence of the 
cartridge. 

Explosive vapor samples were introduced into a 
cartridge from two sources: Vials containing a 
small quantity of explosives and the XonTech 
Model 900 Calibrator. The calibrator is a Pella 
(1976) type and contains two ovens. In the first 
oven the explosive is maintained at a constant tem¬ 
perature so that the explosive will have an equilib¬ 
rium vapor pressure. A small stream (0-50 
cc/min) of inert gas sweeps the vapors into a sec¬ 
ond oven where the sample is diluted with 0-15 
liters of air (see Figure 6). This oven prevents the 
explosive from sticking to the dilution plumbing. 

In the calibrator, approximately 2 grams of 
dynamite was suspended on 20 g of Chromosorb 
G. This material was packed into a 48" x %" O.D. 
FEP column. The column was cooled to 7° C and 
a flowrate 0.5 cc/min of nitrogen was passed 
through the column. The second oven was main¬ 
tained at 40° C. 

The explosives used were all from commercial 
sources in the Los Angeles area. Since we did not 
know the composition of the explosives no at¬ 
tempt was made to calculate a concentration. 
Concentration data presented below represent a 
1 /flow dependence. 

Because the C-4, detasheet, and TNT samples 
were taken from vials, a purge of air equal to or 
greater than the sample flowrate was continuously 
passed through the vial so that the concentration 
was constant. The concentration depended upon 
the permeation rate of explosive out of the sample 
divided by the flowrate. 

RESULTS 

The response of the GC-710 to the dynamite 
emitted from the vapor calibrator is shown in Fig¬ 
ure 7. Over the range of interest the data were 
linear. These data confirm that as the concentra¬ 
tion increases the cartridge will concentrate the ex¬ 
plosive proportionately. 

There was some concern that the cartridge fila¬ 
ment surface area was very small and therefore 
only a small fraction of the explosive could be re¬ 
tained on the cartridges. On the contrary, it was 


432 





















Figure 3. Preconcentrator Valve for the GC-710. 



Figure 4. Experimental setup to check efficiency of sampling cartridge of the Personal Sampler with the GC-710 Explosives Detec¬ 
tor. 


433 















































































Figure 5. Experimental setup showing two cartridges in series and the XonTech Model 900 Vapor Calibrator. 



Dilution Air Input 


Figure 6. Flow diagram of TNT calibration unit. 


434 






































Table 1. XONTECH GC-710 RESULTS OF LABORATORY EVALUATION RESPONSES TO 
PELLANTS 

Materials Source Response (1) 


Explosive 

Composition C-4 

Naval EOD (Old) 


Composition C-4 

14th EOD 


Composition C-4 

USPO 


Composition C-4 

ATF 


Composition C-4 

Naval EOD (New) 


Composition C-4 

Picatinny Arsenal Std 


C-4 

USPO 

S 

Composition B 

Picatinny Arsenal Std 


Composition C-3 

14th EOD 


Swiss sheet 

USPO 


Detasheet, C-3 

14th EOD 

S 

40% Dynamite 

James D. Shea Co. 


Dynamite 


ES 

Detonation Cord (PETN) 

14th EOD 


PETN 

Picatinny Arsenal Std 


PETN 

ATF 


PETN 


LS 

PBX9404 


S 

Black Powder 


LS 

Pistol Powder 


S 

Rifle Powder 


LS 

Black Powder 

Sports Store 


Dupont PB SB propellant 

James Shea Co. 


Dupont 4350 SB propellant 

Sports Store 


Dupont 4320 SB propellant 

Sports Store 


Dupont 4064 SB propellant 

Sports Store 


Dupont 3031 SB propellant 

Sports Store 


Hercules HiVel No. 2 

Sports Store 


DB propellant 

Dupont 4198 SB propellant 

Sports Store 


Dupont 4227 SB propellant 

Sports Store 


Hercules 2400 DB 

Sports Store 


propellant 

Hercules Unique DB 

Sports Store 


propellant 

Hercules Bullseye DB 

Sports Store 


propellant 

RDX, Type Ad 


S 

RDX, Type Bd 


S 

RDX 

U.S. Army 


RDX 

Picatinny Arsenal Std 


HMX 

Picatinny Arsenal Std 


Pentolite 50/50 

Picatinny Arsenal Std 


Tetryl 

Picatinny Arsenal Std 


2,4-DNT 


HS 

2,4-DNT 

Eastman Kodak 


TNT, Recrystallized 


S 

TNT a , Flake 


HS 

TNT a , Powder 


S 

TNT 

Eastman Kodak 


TNT 

U.S. Army 14th EOD 


TNT 

James Cline (TSC) 


TNT 

Hydronautics, Inc. 


Meta-dinitrobenzene 

— 


Para-nitrotoluene 

— 


Dupont Tovex Water gel 

James Shea Co. 



EXPLOSIVES AND PRO- 
Response(2) 


4- Alarm 
+ Alarm 
4- Alarm 
+ Alarm 
+ Alarm 
No Alarm 

+ Alarm 
No Alarm 
+ Alarm 

4- Alarm 

4- Alarm 
4- Alarm 
4- Alarm 


No Alarm 
No Alarm 
4- Alarm 
4- Alarm 
4- Alarm 
4- Alarm 
4- Alarm 

4- Alarm 
4- Alarm 
4- Alarm 

4- Alarm 

4- Alarm 


4- Alarm 
No Alarm 
4- Alarm 
4- Alarm 
4- Alarm 

4- Alarm 


No Alarm 
No Alarm 
No Alarm 
4- Alarm 
No Alarm 
No Alarm 
4- Alarm 


435 



Materials 


Source 


Response (1) 


Response (2) 


Hercules Gel Powder A-2 
Water gel 

Trojan Trogel W-S-7 
Water gel 

Atlas NCN Aqua flow 
Water gel 
Sodium Nitrate 
Monoethanolamine Nitrate 
Methylamine Nitrate 
Ammonium Nitrate 
Ammonium Nitrate 
Diphenylamine-1 
Diphenylamine-2 
Diphenylamine 
Ethylcentralite-1 
Ethylcentralite-2 

Inflammables 
Diesel Fuel 
Kerosene 

Unleaded Gasoline 

Acetone 

Gasoline 

No. 2 Diesel Fuel 

Methyl Ethyl Ketone 

Nitrobenzene 

Nonexplosives 

Aftershave 

Antiperspirant 

Carbon tetrachloride 

Fertilizer 11 

Preshave 

Shoe polish 

Smoke, cigarette 

Snopakec 

Snopake Solvent 

Zerex Antifreeze 

Jaurellue Perfume 

Fabulous Perfume 

Old Spice After Shave 

Trichloroethylene 

Carbon Tetrachloride 

S. S. Pierce Lavender Refresher 

Exhaled cigarette smoke blown 

into inlet 

Burning cigarette held at inlet 


James Shea Co. 

James Shea Co. 

James Shea Co. 

Mallinkrodt Chem. 

Hercules Chem. Company 
Dupont 

Matheson, Colleman, Bell 

NAVALEOD 
NAVAL EOD 

Mallinkrodt Chem. Company 
NAVAL EOD 
NAVAL EOD 


+ Alarm 
+ Alarm 
+ Alarm 

No Alarm 
No Alarm 
No Alarm 
No Alarm 
NR 

No Alarm 
No Alarm 
No Alarm 
No Alarm 
No Alarm 

NR 

NR 

NR 

No Alarm 
No Alarm 
No Alarm 
No Alarm 
No Alarm 

NR 

NR 

NR 

NR 

NR 

NR 

NR 

NR 

NR 

NR 

No Alarm 
No Alarm 
No Alarm 
No Alarm 
No Alarm 
No Alarm 
No Alarm 

+ Alarm 


* Abbreviations: ES, extreme sensitivity; HS, high sensitivity; S, sensitivity; LS, low sensitivity; NR, no response. 
a It is most likely the DNT content of these samples cause an alarm. 

b Fertilizer mixture: N = 12%, Fe = 3%,S = 8%, phosphoric acid = 6%, potash = 4%, balance is inert filler. 
c Contains large quantities of perchloroethylene. 
d These samples contain a trace of TNT. 

(1) Chapter 6 “Entry Control System Handbook”, Sandia National Labs, June 1980 

(2) Hobbs, John, “Evaluation of XonTech (Xonics) GC-710 Explosives Detector” FA A, DOT, Cambridge, Mass (1981) 


found that sufficient explosive could be collected 
on the cartridge to completely remove all of the 
standing current when the explosive alarm peak 
eluted from the column. 


Tests were conducted to determine the adsorp¬ 
tion coefficient of the cartridge. The adsorption 
coefficient of the cartridge, P,, is defined as 


436 




Pf = — (1) 

R. 

Where R, is the response of GC-710 using an 
uncoated cartridge and R; is the response of the 
GC-710 using an activated cartridge. The coated 
cartridge is reactivated by placing it in the GC-710 
and heating the filament. Experimentally, the ad¬ 
sorption coefficient was determined by placing a 
coated activated cartridge between the source of 
explosives and the GC-710 as shown in Figure 5. 
When the sample was drawn through the activated 
cartridge the results compared with those obtained 
using an uncoated cartridge (filament of platinum 
was not chemically coated), the results shown in 
Table 2 were obtained. 

To demonstrate the dependence of sample time 
on the retention of various explosives picked up by 
the cartridge, samples were taken for different 
sample times at a constant sample flowrate from a 
source of explosives at a constant concentration. 
These data are shown in Figure 8. 

Sampling a constant concentration of dynamite 
at various flowrates showed an increase to the in¬ 
strument response at the higher flowrates. The 
data in Figure 9 reflect these data. The GC-710 
Explosive Detector samples at ~ 350 cc/min. 
These data indicate that while both the Explosive 
Detector and Personal Sampler sensitivities may 
be increased by increasing the flowrate, restric¬ 
tions due to weight and battery power presently 
limit this flowrate. 



RELATIVE DYNAMTTF MNrFNTRATinN 

Figure 7. GC-710 response as a function of dynamite concen¬ 
tration. Sample flow is 330 CCM for 10 sec. 


Table 2. ADSORPTION COEFFICIENTS FOR VARIOUS 
EXPLOSIVES ON GC-710 CARTRIDGE 

Adsorption 

Explosive Coefficient 


DYNAMITE 

0.64 

C-4 

0.45 

DETASHEET 

0.44 

TNT 

0.45 



Figure 8. Response of GC-710 to various sample flow times. 
Sample flow is 330 ccm. 



Figure 9. Response of GC-710 to various sample flows for a 
constant source of explosive. 


437 
















When sampling with the Personal Sampler, care 
must be taken to prevent contamination of the un¬ 
used or previously sampled cartridges and the po¬ 
tential loss of the explosive sample. For this rea¬ 
son XonTech recommends that each cartridge be 
placed in an inert cartridge holder whenever the 
cartridge is not in the instrument. Figure 10 shows 
four of these cartridge holders attached to a clip 
board. 

With the use of these holders it was found that 
loss of explosives due to a waiting period between 
sampling and analysis was reduced. Waiting 
periods up to 30 minutes can be tolerated, as 
shown in Table 3. 

The actual sampling time was investigated to see 
if the time an explosive was found during a search 
made any significant difference in the results. As¬ 
suming a searcher would use the sampler for one 
minute (sample pump runs for an integrated sam¬ 
ple time of one minute), a test was made to deter¬ 
mine if there was any difference due to sampling 
the explosive during any 10-second period of the 
one minute sample time. These data are shown in 
Figure 11. The results show little difference due to 
the sampling time. 

These tests were repeated for dynamite over a 
two minute integrated sampling period. It was 
found that the response was significantly reduced 
by the additional minute of sample time. 

APPLICATIONS 

In actual applications the Model 7101 Personal 
Sampler may be carried easily by a searcher to sys¬ 
tematically search an area or room. For such a 
search XonTech recommends that two to five Per¬ 
sonal Samplers be used with four (4) or five (5) 
cartridges. Figure 10 shows a search in progress. 
As the searcher proceeds around a room he/she 
would fill out a search record similar to one shown 
in Figure 12. The record shows what was searched 
with each cartridge. To preclude an excessive sig¬ 
nal due to sampling a source of explosive for up to 
one minute, or the loss of signal due to excessive 
sampling time, XonTech recommends the use of a 

Table 4. IMPACT OF PERSONAL SAMPLER 

1 GC-710 Unil 


Table 3. LOSS OF EXPLOSIVE DUE TO WAITING AF¬ 
TER A SAMPLE IS TAKEN. 

Response on GC-710 


Waiting Time, min Dynamite C-4 


1 5 2.5 

5 4 

10 4 

30 4 2.2 



Figure 10. Explosive search with Personal Sampler and four 
cartridges attached to clipboard with notes for search record. 


maximum one minute integrated sample time for 
each cartridge when using the Personal Sampler. 

Upon completion of the sampling, the clipboard 
with cartridges is returned to the instrument tech¬ 
nician who examines each cartridge in the 
GC-710. The examination reactivates the car¬ 
tridge so that it may be re-used. The searcher 
merely exchanges clipboards and continues to 
search. Figure 13 shows an exchange being made. 

The instrument technician fills out an Explosive 
Analysis Record (Figure 14) for each analysis. 

1 GC-710 Unit 
w/5 Personal Samplers 

5 GC-710 Units and 20 Cartridges 


Weight, Pounds 43 

Approx. Cost ($) 10,000 

No. of Searchers 1 

No. of People Required 1 


215 

50,000 

5 

5 


50 

18,000 

5 

6 


438 









Figure 11. Response of Personal Sampler to a 10 sec exposure 
of various explosives at varying times during a 60 sec sample. 

EXPLOSIVE 
SEARCH RECORD 



Figure 13. Exchange of samples and analysis of cartridges with 
XonTech GC-710 Explosive Detector. 


Facillty 

^3 1 ^ 


Dat 




Search clockwise around the room (left to right) after you check 
air ducts. 


Cartridge No. 
1. 


Search Areas 


input airduct. Ex ha ust a 1 rd uc 

<rv^ uj-*JUL 


'Z$CrC>)(zLjLdj*j& r , 'S jq JLol^CEo^. 


Facility 


Room 

Cartridge 

Alarm 

>3/7 

/ 

^/o 

,3/7 

>2 


2/1 

2 

-ASo 

2/7 

+ 

^/o 

-3/(o 

/ 

^/o 

-3/ & 

JL 

^A/o 

2/(? 

2 



4 





Meter Indication 





Unusual Packages 


Operator 


Searcher__ 

Figure 12. Explosives Search Record. 

Any unusual results can be noted for a request tor 
an additional search. 

The GC-710 can analyze one sample every 15 
seconds. Thus, five searchers using four cartridges 
each can keep the GC-710 busy. 


Figure 14. Explosive analysis record. 

Another application for a Personal Sampler 
may be to search personnel who cause an alarm to 
occur in a walk-through screening portal. Figure 

15 shows a person entering the XonTech Model 
712 Personnel Explosives Screening Portal. Figure 

16 shows him being searched with the Personal 
Sampler after the screening portal has alarmed. 


439 
























Figure 15. XonTech Model 712 Personnel Explosive Screening 
Portal. 



Figure 16. Personnel search after an alarm on the Personnel 
Explosive Screening Portal. 


CONCLUSIONS 

The state-of-the-art of explosive detection 
using the GC-710 Explosive Detector allows the 
detection of most organo-nitrate compounds. The 
Personal Sampler makes possible the easy porta¬ 
bility, collection, and preconcentration of explo¬ 
sives in a search device. The data presented here 
shows that a large area can be checked by the use 
of multiple cartridges and multiple Personal Sam¬ 
plers. The impact of the sampling of explosives 


with multiple, portable preconcentrating car¬ 
tridges is shown in Table 4. The cost reduction and 
weight reduction is a factor 3 and 4 respectively. 

REFERENCES 

Pella, P. A. (1976), “Generator for Producing 
Trace Vapor Concentrations of 2,4,6-Trinitro¬ 
toluene, 2,4-Dinitrotoluene, and Ethylene Gly¬ 
col Dinitrate for Calibrating Explosives Vapor 
Detectors’’, Anal. Chem. 48, 1632. 


440 
























REMOTE DETECTION OF EXPLOSIVES 
USING TRAINED CANINES 


James C. Smith 

Allied-General Nuclear Services 
Post Office Box 847 
Barnwell, South Carolina 29812 


ABSTRACT. Through investigative research, Allied-General Nuclear Services, 
operating under contract to the U.S. Department of Energy, has developed a facili¬ 
ty and technique for the remote detection of explosives. This work generally in¬ 
volved the remote searching of personnel entering sensitive areas of a facility. The 
work was generic in nature and the results can be applied to any situation where the 
carrying of explosives on personnel constitutes a threat. In that this system utilizes 
a remote detection concept, it does not violate individual civil liberties. The devel¬ 
oped system involves placing the search subject in a booth and circulating a volume 
of filtered and air-conditioned air across and around the subject. The booth air is 
also recycled to assure proper mixing and minimum dilution. The booth air is ex¬ 
hausted and a sample of the air stream extracted by way of an isokinetic sampler. 
This sample of air is investigated by a trained canine in an area divorced from the 
search subject. Trained canine response indicates the presence or absence of explo¬ 
sive odors. While a number of explosives have been investigated using this remote 
detection concept, Commercial Dynamite and C-4 were used in full testing. Re¬ 
sults showed nearly 100% detection and an error rate of less than 2%. Testing was 
conducted using small concealable samples of two to four ounces. Processing time 
during testing was twenty to thirty seconds per four-person group. Through ancil¬ 
lary tests, certain limitations of canine use in explosive detection were revealed. 
These involved odor concentration and discrimination problems. Methods of mini¬ 
mizing and overcoming these problems have been addressed and will be discussed. 


REMOTE DETECTION OF EXPLOSIVES 
USING TRAINED CANINES 

For the past five years or so, at its Barnwell 
Nuclear Fuel Plant, Allied-General Nuclear Serv¬ 
ices has been doing some very interesting work in 
the area of Nuclear Material Safeguards under 
contract to the U.S. Department of Energy. 
“Safeguards,” for those of you who may not be 
familiar with the term, is a two-sided function 
somewhat peculiar to the nuclear industry. One 
side is involved in the monitoring of Special Nu¬ 
clear Material (plutonium or highly enriched 
uranium) in a processing facility and accounting 
for this material. The other side of Safeguards is 
the Physical Protection of the facility itself and 
the Special Nuclear Material within it. The physi¬ 
cal threats protected against are sabotage (those 
acts which would disable the facility and/or cause 


radiation to be released, thereby posing a danger 
to the general public), theft of Special Nuclear 
Material (the overt or covert theft of large quanti¬ 
ties of material by insiders and/or outsiders), and 
diversion of Special Nuclear Material (the theft of 
small quantities of material usually by an insider 
and usually over a long period of time). 

1 would like to discuss with you today the work 
we have done in one area on the Physical Protec¬ 
tion side of Safeguards, dealing with the threat of 
sabotage in particular. Most acts of sabotage in¬ 
volve the use of explosives. As part of the control 
of personnel access to sensitive areas of a nuclear 
facility, operators of such facilities have the re¬ 
sponsibility to assure that explosives and other in¬ 
cendiaries do not enter these areas. Large quanti¬ 
ties are not of great concern because visual inspec¬ 
tions will generally reveal attempts to carry these 


441 


large quantities through an access control point. 
What is of concern, however, is the carrying-in of 
small, concealable quantities which could be 
cached inside, and later gathered and formed into 
a device that could cause significant damage. 

Our mission was to develop a system of search¬ 
ing personnel for small amounts of explosives with 
a high degree of accuracy in a cost-effective and 
expeditious manner. There are, of course, several 
alternative methods available to approach this 
mission. One alternative was to conduct universal 
or sporadic “pat-down” searches of employees. 
This was fairly quickly discounted for two pri¬ 
mary reasons. First, to provide for expeditious 
movement of personnel especially during a shift 
change, a large number of both male and female 
security personnel are required for “pat-down” 
searches. This is both costly and presents security 
manpower scheduling/use problems. Secondly, 
and more importantly, the use of physical 
“pat-down” searches could be construed by em¬ 
ployees as a personal affrontal which would pre¬ 
sent serious Employee Relations problems. 

Another alternative is the use of explosive detec¬ 
tion instruments using electron-capture technol¬ 
ogy or the more recently developed gas-chro¬ 
matography instruments. These devices are cur¬ 
rently in use at many nuclear facilities but their use 
is subject to some reservations by operators and 
regulatory agencies alike. The reservations are the 
high cost of these instruments and the low proba¬ 
bility of detection on some explosive compounds 
(like C-4 and Black Powder). Another concern is 
the time factor necessary to assure an acceptable 
probability of detection level. The hand-held units 
appear to be more accurate than the walk-through 
portal units, but are more expensive and slower. 
Therefore, more units and personnel are required 
to process large numbers of personnel expeditious¬ 
ly. 

In our work, we studied a search method com¬ 
bining a system of accuracy (high probability of 
detection), speed of search (a goal of less than 30 
seconds per employee), and cost. In that canines 
had a long history in bomb detection work, we 
first investigated work done by others. This led us 
predominantly to the U.S. Air Force, Sandia 
Labs/Southwest Research Laboratory, U.S. Cus¬ 
toms, and several European law enforcement 
agencies. We found that the canine olfactory sys¬ 
tem had great potential for our application. Addi¬ 
tionally, the canine possessed other attributes that 
made it even more attractive. A dog is portable 


and therefore could be used in various locations. 
He adapts well to environmental change (in¬ 
side/outside). He is capable of many tasks beyond 
explosive detection and therefore potentially had 
more “use time” which increased his cost effec¬ 
tiveness. The canine also had some drawbacks, of 
course. He requires initial training, reinforce¬ 
ment-training, care, and maintenance. The canine 
presented another potential problem—that of em¬ 
ployee problems and civil liberties problems if the 
dog was exposed directly to employees. But, over¬ 
all, it appeared to us that when properly managed, 
the dog represented a potentially valuable and cost 
effective tool. We felt that the Employee Relations 
and civil liberties problems could be precluded 
through proper design and management. 

After investigation, we concluded that the 
canine could be used for explosive screening of 
personnel and many other things, but that it was 
imperative that the dog be in a position remote 
from employees and employee traffic. The prob¬ 
lem then became: “Keep the dog away from the 
people and somehow transport the scent from the 
employee at physical point “A” to the canine at 
remote physical point ‘B.’ ” 

There ensued a very interesting evolution of de¬ 
sign, training, and behavioral study. For this dis¬ 
cussion I shall concentrate primarily on facility de¬ 
sign. 

Our first attempt was what we now fondly call 
“the closet portal.” In this phase of our work, we 
placed the dog and handler in a “closet” with a 
floor which was five feet by six feet. The search 
subject stood in a verticle “telephone booth”-like 
affair which was affixed to the outside of the 
“closet” door (Figure 1). The search subject 
“box” had air holes placed in such a manner that 
air would be drawn across all parts of the search 
subjects body, and passed through the “closet 
door” via a four-inch diameter “scent port” ap¬ 
proximately 20 inches above floor level. The 
“air-handling” equipment was a variable speed 
drum blower with a maximum of 350 scfm 
mounted on the rear wall of the “closet” and 
exhausting air out of the closet. The air flow pat¬ 
tern then was from the room, through the “tele¬ 
phone booth,” through the “scent-port,” and 
finally through the “closet” and out the wall to 
the outside. This arrangement had one very ser¬ 
ious flaw in design: the confinement of the 
“closet” did not permit the dog to move while 
working, which, we found most dogs prefer to do. 
Moreover, the close confines of the “closet” 


442 



Figure 1. 


caused the animal, out of courtesy I am sure, to 
occupy the least space possible—which is a sitting 
position. This unfortunately coincided with his 
“alert” position—which is also sitting. It was 
somewhat obvious, however, that the dog was de¬ 
tecting the explosive odors when present and, of 
course, when his attention was directed to his 
work. Therefore, we concluded that the theory 
held promise, but the facility design was almost 
totally inappropriate. 

From the “closet,” we advanced to the first real 
set of booths. We constructed four booths of 
heavy plywood and coated them with an epoxy 
paint inside and out. The booths were approxi¬ 
mately three feet square and seven feet high inside 



SO 5 

^ 5 ? 

<&p 


L z^xr J 

424 4#4 

-i- 


44 = 


#■ 

n 

_ 




iiii^ 


First Booths 

Figure 2. 


(Figure 2). The epoxy coating was recommended 
by Sandia Laboratories and provided us with a 
very cleanable surface from which to remove resi¬ 
dual explosive odor. The booths had locking 
doors with a sealing medium to prevent air from 
leaking out of the booth. Air was supplied from 
the variable speed blower mounted on top of each 
booth. The air was taken from the room, blown 
down upon the search subject and back out into 
the room through a “scent-port” located at the 
back side of the booth and approximately 20 
inches above floor level. The “ports” were cov¬ 
ered with wire mesh to “protect” the search sub¬ 
ject from the canine. Behind the row of booths 
was an area 5 feet wide and 20 feet long. This pro¬ 
vided adequate room for dog and handler to 
work. In a short time, the routine for searching 
each scent-port was established with the canine. 
We started with positive and negative plants 
placed about one foot off the floor of the booth. 
Fairly quickly, we had indications of much im¬ 
proved detection rates. They were on the order of 
85 to 90% and a 10 to 15% false alert rate. Then 
we introduced people into the booths in sets of 
four. The detection rates went down and the false 
alert rates went up. 

To summarize this test phase, we found the fol¬ 
lowing: 

(a) The dog was falsely alerting on food, 
cosmetics, and other unknown personal odors. 
This was later eliminated by a period of avoidance 
training. 

(b) We believe that the reduced detection level 
was also caused by longer test periods and a result¬ 
ant buildup of explosive vapors in the room due to 
exhausting the booth air into the room and recy¬ 
cling that air back through the booth. As a tempo¬ 
rary remedy to this, we set a large fan at the back 
door of the room and pulled air through the 
opened front door. This helped but did not totally 
solve this problem. 

(c) We found that we were getting a very 
laminar flow of air from the blower-port down 
across the subject which tended to hamper a 
“whole booth” sample of air. A subject could 
hold the sample near a wall and we would miss it. 
We tried several diffuser designs at the inlet port 
and this helped. We also installed “whisper fans” 
on two opposite inside corners of the booth 
pointed 45 degrees to the wall and 45 degrees to 
the floor. The whisper fans and the mixing of air 
they provided aided considerably in bringing the 
detection rate up. 


443 





















































(d) We found that air velocity at the scent port 
was most critical. If it was too low, there was not 
enough vapor for the dog to sample. If the veloc¬ 
ity at the scent port was too high, it seemed to dis¬ 
turb the dog’s whiskers to a point where he would 
actually avoid the scent port due to the discom¬ 
fort. Additionally, high velocity tended to dilute 
the explosive vapors thus reducing probability of 
detection. We briefly tested the system using air 
flows ranging from 0.6 scfm to 30 scfm. We found 
a composite “comfort range” and “minimum 
odor dilution level” to be 7 to 9 scfm. 

(e) We found that lingering or residual odor 
was a problem for it usually resulted in a false 
alert on the next pass. Extensive “flushing” of the 
booth with air is essential in reducing or eliminat¬ 
ing this problem. The flushing time necessary is a 
function of the size of the booth, the finish on the 
booth walls, the type of explosive and, of course, 
the amount of air passing through the booth. In 
the booths described in this phase, we found that 
nearly three minutes of flushing at approximately 
300 scfm were necessary to reduce residual odor 
from a small explosive sample to a working level. 

(0 We also concluded during this phase of our 
work that humidity level was a factor affecting lin¬ 
gering or residual odor. The higher the humidity, 
the longer the “flushing period” required. No 
definitive correlative data were developed however 
(Figure 3). 

In all, this second stage of experimentation was 
most revealing. As we discovered and corrected 
(to the extent possible) the problems, we saw the 
detection level consistently improve to the 90-95% 
level and false alerts decrease to the 4-7% range. 

Problems 

A. False alerts on food, cosmetics, etc. 

B. Room contamination reduces detection level 




Scent portals 
and platform 
I 


14 





Equipment 

room 





Vapor 

transfer pipe 

X 





r 


Subject 

"booths 


1 


1 


Canine Evaluation Test Trailer 

Air Flow 


Figure 4. 


Again, armed with a plethora of facts, conjec¬ 
tures, and ideas, we entered into the next phase of 
our experiment. We concluded that the row of 
four booths had served its purpose and proceeded 
to refine our design in another area which would 
provide heavier personnel traffic for full testing of 
this concept of remote explosive screening. We 
leased a 12-foot by 40-foot trailer. We placed the 
personnel search portal in one end and the detec¬ 
tion scent ports in the other end of the trailer (Fig¬ 
ure 4). On the personnel end of the trailer, we pro¬ 
vided doors on both sides of the trailer for 
two-directional, walk-through traffic. We in¬ 
stalled four booths of the same size, construction, 
and finish as in the earlier phase. We added plexi¬ 
glass panels to the doors to accommodate 
“claustrophobic” complaints that we had received 
from employees during the earlier test. We also 
later installed a CCTV monitor in full view of all 
the booths so personnel could watch the dog work 
in the other end of the trailer. This kept employee 
interest up during these sometimes boring and in- 
terruptive testing periods (Figure 5). 

In the other end of the trailer (the scent port 
room), we installed four “boxes” along the wall 
separating the air handling equipment in the mid¬ 
dle of the trailer (Figure 6). These boxes were one 
foot cubes, approximately 55 inches above floor 
level. Each box had a three-inch inlet hole in the 


C. Laminar air-flow resulting in “dead spots” at walls 

D. Scent port air velocity- 

low = reduced available vapor - low detection 
high = discomfort to canine - avoidance 

E. Lingering, or residual odor causing false alerts 

F. Humidity necessitates longer “flush” time 

« 13 - 05-5 



Canine Evaluation Test Trailer 

Traffic Flow 


Figure 3. 


Figure 5. 


444 























































































12-ft.x 40-ft. 

Figure 6. 


bottom and a four-inch outlet hole in the top. The 
exposed face of the box was open to the full 
12-inch by 12-inch inside dimension (Figure 7). 
Directly in front of the row of scent ports, we in¬ 
stalled a 2 l /2-foot walkway for the canine 30 



inches above the floor level. This enabled the han¬ 
dler to work the canine without stooping over. 
Ramps at right angle to the walkway were installed 
at each end to allow the dog easy and safe access 
to and egress from the walkway. Floor and walk¬ 
way surfaces were carpeted for noise abatement 
and safety. 

The air movement system was a good deal more 
complex than in the earlier phases of our work 
(Figure 8). Fresh air was drawn from the outside 
and drawn through a HEPA filter by a 500-scfm 
drum-type blower. The main air supply was mani¬ 
folded into four 4-inch booth supply pipes. Each 
pipe was attached to the false top of a booth which 
served as a booth supply plenum. The booth sup¬ 
ply plenum fed four vertical three-inch PVC pipes 
located in the corners of the booth. The vertical 
pipes were closed at the booth floor. Holes one 
inch in diameter were drilled in the vertical pipe 
pointing toward the middle of the booth where the 
search subject would stand. A three-inch stainless 
steel booth exhaust pipe was attached to the back 
of each booth one inch above the floor level (Fig¬ 
ure 9). Exhaust air from the booth traveled ap¬ 
proximately twenty feet through the air handling 
equipment room in the middle of the trailer. Ap¬ 
proximately five feet short of the wall separating 
the equipment room from the scent port room, the 
booth air exhaust pipe was turned upward in a 
gentle 48-inch radius, 90° turn. At the point of the 
turn, a one-inch diameter isokinetic sampler was 
welded into the three-inch stainless steel pipe with 


445 









































^Adjustable damper 
E- Flow measuring connection 


Exhaust 
to outside 


Exhaust 
to outside 


Outside. 

air 



500 SCFM 0 5-in. H 2 0 


Air Handling System 



Figure 9. 


Figure 8. 

an inside protrusion of 1 Vi inches. The other end 
of the isokinetic sampler was attached to a reducer 
on the bottom of the scent port box. The main 
four-inch booth exhaust pipe was terminated out¬ 
side the roof of the trailer and exhaust air released 
to the environment. 

Control dampers were installed at strategic 
points in the system to: 

(a) Control booth supply air at 100 scfm 

(b) Control main exhaust air at 92 scfm 

(c) Control sample air to scent point at 8 
scfm. 

We also installed a second exhaust blower to 
handle the scent port box exhaust air. This was a 
100-scfm drum-type blower manifolded on the in¬ 
take side to the tops of the scent port boxes. 
Dampers between the scent ports and the manifold 
controlled air flow to 10-12 scfm. The exhaust 
side of the blower was directed outside to the envi¬ 
ronment. What resulted here was the exhausting 
of the 8-scfm sample tube air along with a small 
amount of scent port room air thereby precluding 
vapor contamination of the scent port room itself. 

Once we became familiar with the system, we 
found that we could start up the system, subse¬ 
quently adjust air flows in approximately 15 min¬ 
utes, and periodically check them in about five 
minutes. We recommend communications ability 


446 

































from the air handling equipment room to both the 
personnel booth area and the scent port room 
since in our design some of the control dampers 
are remote from measuring points. To calibrate 
the system, we used an anemometer and stop 
watch. 

Before testing this design, we devoted approxi¬ 
mately two weeks to acclimating the canine and 
handler to the scent port room routine, to training 
the personnel who would conduct the test, and to 
orienting the employee group to their search-sub¬ 
ject role in the test. We chose C-4 (4 ounces) and 
Commercial Dynamite (20 ounces) as the explo¬ 
sives for the test. All samples were to be hand-car¬ 
ried in waxed paper for this text. Additionally, all 
search subjects were to carry a piece of waxed 
paper into the booths. With the help of a statisti¬ 
cal consultant, we structured the test and used a 
random sample schedule prepared by him. The 
sample schedule provided an overall frequency of 
approximately one-in-nine plants. Samples and 
waxed paper were issued to employees some 50 
feet away from the trailer and recovered at 
another point away from the trailer. Search sub¬ 
jects were placed in the booths in groups of four in 
numerical trial order under the supervision of test 
personnel. Air was allowed to circulate over the 
search subjects for 30 seconds prior to the search. 
After this 30 seconds, the canine sampled the air in 
each of the scent port boxes in the other end of the 
trailer. If an alert ensued, the canine handler 
moved a switch corresponding to the alerted upon 
booth scent port which illuminated a booth num¬ 
bered light in the other end of the trailer. The re¬ 
maining scent port boxes were then investigated by 
the canine. All positive and negative responses 
were recorded on data sheets which were given to 
the statistician for analysis. In addition, the tests 
were monitored by our Quality Assurance group 
to ensure strict conformance to the approved Test 
Plan. The results of this test most encourag¬ 
ing (Figure 10). 

On the Commercial Dynamite: 

Total Number of Trials 
Number of Explosive Plants 
Detection Rate 
False Alert Rate 
Total Correct Rate 
On the C-4 : 

Total Number of Trials 
Number of Explosive Plants 
Detection Rate 
False Alert Rate 
Total Correct Rate 


720 

102 

102 / 102 —( 100 %) 
18/618—(2.9%) 
702/720—(97.5%) 

420 

64 

64/64 —(100%) 
7/356—(1.9%) 
413/420—(98.3%) 


These test results reflected a marked improve- 


Phase Two Results 

COMMERCIAL DYNAMITE 


Total number of trials 

720 


Number of explosive plants 

102 


Detection rate 

102 

(100%) 

False alert rate 

18 

(2.9%) 

Total correct rate 

702 

(97.5%) 


C-4 


Total number of trials 

420 


Number of explosive plants 

64 


Detection rate 

64 

(100%) 

False alert rate 

7 

(1.9%) 

Total correct rate 

413 

(98.3%) 



83 / 13 - 05-34 


Figure 10. 

ment over the previous phase. We attribute this 
improvment to the facility design. 

We did notice some design deficiencies during 
the pre-test and test, however. 

(a) During rainy or very humid periods, the 
paper HEPA filter element collected moisture 
which restricted air flow. 

(b) The temperature of the air blowing across 
the search subjects was at outside ambient tem¬ 
perature which provided discomfort on occasion 
(i.e., winter mornings and summer afternoons). 

Both of the above problems are solvable with 
the installation of an air conditioning system 
ahead of the HEPA filter which would assure con¬ 
stant control of humidity and temperature. This 
air conditioning system must be of the 
“once-through” design rather than the normal re¬ 
circulating type with minimal makeup air. This is 
necessary to preclude the recirculation of explo¬ 
sive-vapor-contaminated air. 

(c) While the air in the search booths was mix¬ 
ing well, there were some “dead spots” along the 
walls of the booth. We were concerned that it 
might be possible to hold very small amounts of 
explosives in these areas and avoid detection. This 
was, in the next phase of the test, easily overcome 
by drilling !/ 2 -inch holes in the vertical air supply 
pipes in the booths. These holes were placed in 
such a direction as to force air along all four walls 
inside the booth and in a similar direction (Figure 
11 ). 

There was another concern. In addition to the 
booth air mixing matters that we had been work- 


447 


Problems 

A. Humidity 

B. Temperature 

C. “Dead-spots” 

83 / 13-05 35 

Figure 11. 

ing on, we wondered whether the “once-through” 
air flow design incorporated in the system was 
over-diluting explosive vapors in the system when 
they were present. Based on the results from the 
previous phase of testing, there was no reason to 
believe that this was the case. However, because of 
our concern of very small amounts of explosives 
carried, we decided to recirculate the booth air in 
an attempt to minimize dilution and, at the same 
time, enhance the air-mixing function. To do this, 
we installed four blowers, one for each booth. The 
blowers were constant speed and rated at 75 scfm. 
Air was drawn from two 6-inch ports eight inches 
above booth floor level, manifolded down into 
one stream, through the blowers, re-manifolded 
back into two 6-inch pipes and then back into the 
booth eight inches below the booth ceiling level. 

Unfortunately, the test schedules did not permit 
the installation of an air conditioning system prior 
to the third and final testing phase. As a result, we 
are unable to statistically confirm our conjecture 
on this point. 

During the final testing phase, we held to the 
same test structure with the physical modifications 
mentioned earlier and two notable exceptions. 
This phase of testing was to determine the effects 
on detection rate and false alert rate when the ex¬ 
plosive sample was wrapped and concealed. (You 
will remember that the samples were “hand-held” 
in the earlier phase.) In the final phase, four 
ounces of C-4 were wrapped in heavy gauge, poly¬ 
ethylene bags and concealed in the pockets of 
clothing. The samples were again randomly placed 
during the test, and bags were present in all trials. 
Also, the samples were held in the clothing for 
randomly selected five-minute time increments 
ranging from 5 minutes to 20 minutes prior to 
search. (C-4 was selected because of its low vapor 
pressure and by request of several federal agen¬ 
cies.) We also reduced the pre-search booth time 
from 30 seconds to 20 seconds. Budget considera¬ 
tions prevented the testing of more than one ex¬ 
plosive type. 


The results of this testing phase were as follows: 


Total Number of Trials 

200 


Number of Explosive Plants 

29 


Detection Rate 

29/29 

— 100% 

False Alert Rate 

1/171 

—0.6% 

Total Correct Rate 

199/200 

—99.5% 

Likely Bounds (approximately 95% confidence 
limits) 

Total Correct Rate 

96.8 

— 100% 

Detection Rate 

85.4 

— 100% 

False Alert Rate 

0.3 

— 4% 


Figure 12. 


It should be noted that the likely bounds are low 
because of the small number of samples and trials 
in the test. 

We are therefore assuming that this approach to 
remote personnel searches for small amounts of 
explosives provides promising results that meet 
our criteria of high probability of detection (ap¬ 
proximately 100%), low false alert rates (approxi¬ 
mately 1%), and expeditious searching of large 
volumes of people (approximately 20-25 seconds 
per group of four in the test). [Note: We feel that 
eight to ten people could be search in eight to ten 
booths within the 20 to 30 second time frame]. Fi¬ 
nally, it appears to be cost effective (one dog and 
handler during periods of high traffic and one of¬ 
ficer and one instrument during low traffic pe¬ 
riods). 

As a result of some informal testing, and par¬ 
ticipation in tests conducted by others, we offer 
some insights to canine-team limitations and pro¬ 
gram structure. 

(1) The same system appears useful for narcot¬ 
ics odors. 

(2) For facility operation in all whether condi¬ 
tions, an adequate supply-air conditioning system 
is essential. 

(3) If the canine is to alert on both large and 
small explosive samples, inside and outside, he 
must be trained on both large and small samples, 
inside and outside. 

(4) The canine works best “moving” and work¬ 
ing continuously. The working environment 
should be non-confining and active. 

(5) Training aids can become cross-contami¬ 
nated. They should be stored separately and 
worked separately. 

(6) The search team, in an access portal, should 
be under knowledgeable surveillance. Consistency 
of speed and commands is important to preclude 
confusion and boredom in the canine. 


448 


(7) The canine-team approach to personnel 
searches should be used only for high traffic pe¬ 
riods. “On-again, off-again” work is difficult for 
the dog. 

(8) On outside or vehicle explosive searching, 
the experienced handler should plan the search. 


Moving any detector dog too quickly into a strong 
odor is not generally successful. 

(9) A quality training, retraining and certifica¬ 
tion program should be established for canine 
teams. This will provide documented assurance of 
initial and continued proficiency. 


449 






















































THE SCIENTIFIC DEVELOPMENT OF AN EFFICIENT DETECTOR DOG 
THROUGH OLFACTION AND BEHAVIORAL MODIFICATION 


Edward Ernest Dean, D. V.M., M.S. 
and 

Samuel John Tomlinson, Sr., B.S. 

Southwest Research Institute 
San Antonio, Texas 


ABSTRACT. A progressive learning sequence departing from the traditional 
methods of training dogs results in an olfactory sensitive dog compatible with a 
learned behavior to communicate recognition of a primary vapor. In essence, the 
developed dog with a skilled handler becomes a portable, mobile biological vapor 
detector. The innovative procedure researched and practiced at Southwest Re¬ 
search Institute, San Antonio, Texas, emphasizes timely, positive reinforcement of 
desired behavior in qualified dogs. Initial methods sensitizes the dogs olfactory sys¬ 
tem to a practically pure primary odor metered with a nitrogen gas carrier in an 
olfactometer. The dog then learns an associative behavior which communicates 
recognition or discrimination of the primary vapor (explosives, narcotics, etc.). A 
scientifically developed dog, properly managed by an educated handler, can aug¬ 
ment any law enforcement team and in a practical sense excel most known mechan¬ 
ical or electronic detection devices. The discussion will feature a research study on 
the dog’s recognition and olfactory sensitiveness to ethylene glycol dinitrate, an in¬ 
significant component with respect to quantity in five dynamite samples. Some re¬ 
search studies sponsored by the Department of Defense, Drug Enforcement Agen¬ 
cy, Department of the Interior, Department of Agricultural and Industrial Com¬ 
panies will be discussed. Moreover, a casual overview of new work further expand¬ 
ing the usefulness of detector dogs in service to man will be presented. 


A dog developed through the steps of olfactory 
sensitization to a primary odor with concurrent 
behavioral modification compatible to search and 
detection procedures is, in due respect, a vapor 
analyzer. The olfactory dog’s speciality is qualita¬ 
tive rather than quanitative analysis with the capa¬ 
bility of discrete odor discrimination. The dog 
learns in sequence, from positive reinforcement, a 
chain of behavior that eventually directs it to be¬ 
coming a qualified olfactory detector. 

The most difficult and time consuming step in 
the development of an olfactory dog is in limiting 
the negative influence of environmental distrac¬ 
tions. Distractions disrupt its concentration and 
may evoke undesired behavior. Distractions are 
unwanted stimuli. They may be either audio, 
visual, olfactory, tactual or gustatory. The dis¬ 
tractions that are the most disruptive in a practical 
search and detection exercise, especially in a par¬ 


tially trained dog, are audio, visual, and olfaction. 
Olfactory distractions are insignificant when the 
dog becomes accustomed to training. Audio and 
visual distractions, other than the obvious, may be 
very subtle signals from the person working the 
dog. For example, cues from the handler may be 
intentional or unintentional. They may be obvious 
or inapparent. Cues from the handler can cause 
false responses, excitable activity (not to be con¬ 
fused with motivation) or excessive attentiveness 
to the handler rather than the task at hand. The 
dog, because of its close relationship to man, is ex¬ 
tremely susceptible to any cues that might emanate 
from the trainer or handler. With respect to olfac¬ 
tory sensitivity, the dog, compared to man, is a 
privileged animal. In general, a trained dog has a 
sensitiveness on the order of at least one fem- 
tomole (10“ 15 ) and very probably at a much lesser 
concentration. 


451 


A mistake often made by people is concluding 
that dogs are unable to detect chemicals that are 
classed as odorless. This chemical property is in 
respect to human olfaction and not dogs. A dog’s 
olfactory acuity can be developed to perceive and 
discriminate sodium chloride, quinine, heroine, 
some plastic explosives, etc., all of which may be 
regarded as odorless. Myznikev, Pavlov (1958), 
Dean (1973, 1975), Phillips and Dean (1973) It has 
been reported that dogs may detect Vi million dif¬ 
ferent compounds, while humans may detect only 
a few thousand; and, yet, it is recognized that the 
human has a well developed sense of smell. 
Myznikev, Pavlov (1958) 

The dog is classed as a free mouth breather with 
an extremely well developed olfactory system. 
Each nostril communicates with four passageways 
in which air circulates. The nasal septum is on a 
median plane and laterally separates the nasal pas¬ 
sageways. The common nasal passageways lie at 
right angles to the other three. It is the larger of 
the nasal passages; but the middle nasal passage, 
and probably the most significant with respect to 
olfaction, communicates with the cavities of the 
ethmotrubinates which contain most of the olfac¬ 
tory receptors and then continues to the nasal 
pharynx. 

The olfactory nerve is not a single nerve but a 
mass of fiber bundles which arise from the bipolar 
olfactory cells in the nasal cavities. In a morphor- 
logical sense, the olfactory nerve is not a nerve as 
are the other crainal nerves (exclusive of the optic 
nerve) but, instead, is a modified tract of the 
brain. Each olfactory receptor is connected to its 
own nerve fiber which courses uninterrupted with¬ 
out synapsis through the cribriform plate to the ol¬ 
factory bulb which is the forward extension of the 
cerebral hemispheres. The receptors do not termi¬ 
nate in a difuse array but end singly in the glomer¬ 
uli of the olfactory bulb. Wright (1982) 

The ethmoturbinates are bony ridges covered by 
mucous membranes and occupy the posterior half 
of the nasal cavities. This is where the bulk of the 
olfactory cells are located. When the dog sniffs, 
samples of air are forced over the turbinates, ex¬ 
posing the fine cilia in the moist layer of the mu¬ 
cous membrane. It has been observed that a pant¬ 
ing dog with little evidence of sniffing can track a 
victim at a ground temperature of 41 °C and a 
body temperature of 41 °C. This indicates olfac¬ 
tory stimulation via nasal pharynx rather than by 
the nostrils. 

It has been determined that the German Shep¬ 


herd has 2 x 10 9 olfactory receptors and that each 
cell has 125 cilia. Thus, the total ciliary surface 
area is on the order of 7.85 m 2 or several times the 
area of the dog’s body surface area. It has been 
concluded and recognized by olfactory physiol¬ 
ogists that one molecule of a certain vapor is 
enough to stimulate a single olfactory cell. 
Moulton (1976) 

It appears that each receptor cell functions as an 
independent unit through which impulses are car¬ 
ried to the brain. There are many theories on ol¬ 
faction. Of all the expressed theories, there are 
two which are generally acceptable. They are 
Amorre’s chemical theory and Wright’s vibration¬ 
al theory. 

Despite objections in the use of dogs as odor de¬ 
tectors, it is doubtful that while some devices 
might be more sensitive than the dog, they cannot 
at this time, in a practical sense, discriminate 
specific odors as reliably as the dog. A recently de¬ 
veloped bioluminesant technique on the West 
Coast exploiting firefly luciferase as a TNT detec¬ 
tor may offer some advantages, providing an air 
sampling mechanism can be adapted to the lum¬ 
inescent detector for field use. It is claimed that 
bioluminesces can detect TNT at 10“ 18 M. 

The primary objective in using dogs as vapor 
sniffers is to extend man’s capabilities beyond the 
limits of his own. A well trained search and detec¬ 
tor team includes a skilled handler and a skilled 
dog working together. Often the dog is faulted be¬ 
cause of irresponsible handling and inept training 
practices. 

Before submitting the dog to a systematic 
step-by-step learning process, a careful selection 
procedure is necessary. Only about 33% of the 
dogs examined become candidates for about 500 
hours of training. The length of time may vary de¬ 
pending upon the primary odor to be detected, ul¬ 
timate task to be performed, and work environ¬ 
ment. The hours are not massed together but are 
spread out over a 12-month period, working from 
one or more hours per day. The most difficult fea¬ 
ture in training a dog is in coupling its natural abil¬ 
ities to a set of predictable behavioral responses 
acquired through training. It begins with man’s 
ability to shape the dog’s behavior through a 
learning sequence that directs the dog to sniff, 
search and respond to the primary odor in a work¬ 
ing environment. 

The objective is to establish a bond between the 
unconditioned reflexes of the dog to a set of ac¬ 
quired conditioned reflexes. How this is done and 


452 


eventually practiced by an animal behaviorist or 
trainer and handler will influence the reliability 
and performance of the dog. The canine behavior¬ 
ist does not adher strictly to psychology terms but 
uses terms that, in a practical sense, relate to the 
learning period, learning exercises, and work en¬ 
vironment of the dog—much like the teacher re¬ 
lates to his students. 

The characterization that generally makes a dog 
adaptable to training are mediated through the ac¬ 
quired conditioned reflexes (Pavlov). Conditioned 
reflexes are either natural or artificial. The natural 
reflexes are acquired from experiences in associa¬ 
tion with a viable existence. Artificially acquired 
reflexes, in this case, are those learned in the proc¬ 
ess of training. With consistent repetition of train¬ 
ing, the learned response reflex becomes almost 
involuntary (habit). Unconditioned reflexes are 
native to the animal, for example, locomotor re¬ 
flexes, alimentary reflexes, respiratory reflexes, 
pupillary reflexes, etc. Dukes (1977) 

When the dog eats, saliva is secreted. This is an 
unconditioned reflex. Eventually, when the dog 
sees or smells food, it will secrete saliva. This is a 
natural conditioned stimulus. At feeding time, the 
dog learns the noises that are associated with re¬ 
ceiving food. For example, opening the feed room 
door and banging of pans at feeding time will 
stimulate salivation even though the sight and 
smell of food are absent. This reflex is an artificial 
conditioned response. In the development of 
working olfactory detector dogs, food through the 
gustatory reflex (the positive behavior reinforcer) 
is the unconditioned stimulus and the primary 
odor (dynamite, heroin, oil, etc.) is the artificial, 
conditioned stimulus. Before the dog can become 
a working detector, it must learn to search for its 
odor, overcome strong distracting stimuli because 
they, themselves, evoke responses, detect the odor 
stimulus and then signal to the person accompan- 
ing it that the target odor has been found. 

The principal for development of a detector dog 
is to shape its behavior to the limit that the learned 
response becomes nearly habitual. The dog is in¬ 
doctrinated with small bits of food following the 
performance of acceptable behavior. The verbal 
praise, good, is paired with food reinforcement 
which is similar to the dog’s artificially condi¬ 
tioned reflex of salivating when it hears the sounds 
associated with daily feeding preparations. The 
verbal praise ultimately has three purposes: 

(1) A convenient positive reinforcer in lieu of 
food (which should not be extensively practiced) 


(2) A stop-gap between the time of response 
and serving of food reward—This is more impor¬ 
tant in the beginning steps of training. The delay 
between verbal good and serving of food should 
be minimal. It is important that the verbal an¬ 
nouncement and serving of food be accomplished 
by the trainer so that this operation is in two dis¬ 
tinct steps. If the trainer reaches for the food be¬ 
fore announcing “good”, the dog will surely cue 
on the handler’s hand. If the handler feeds the dog 
at the same moment he announces “good”, the 
verbal reinforcement will become meaningless. 
When the dog becomes familiar with the routine 
(search, detect, sit, verbal “good”, feed), the time 
between the verbal reinforcement and serving of 
food can be extended from one or two seconds to 
five or six seconds. When the delay time of five or 
six seconds, the dog might verify or re-examine 
the positive odor. A longer delay time may cause 
the dog to become impatient. 

(3) To facilitate learning when the primary 
odor is nonvolatile—This is the most difficult 
form of use of verbal praise. The dog’s nose must 
be positioned over the odor and a “precision 
guess” that the dog is sniffing at the time the ver¬ 
bal “good” is announced. In a series of trials, the 
watchful trainer will, on chance alone, announce 
verbal “good” in a timely manner so that the pur¬ 
pose of the cue will become meaningful to the dog. 
As with any expedient, the verbal cue should not 
be overused. 

A simplified laboratory behavioral chain is dia¬ 
grammed to illustrate the alternate management 
of behaviors during learning exercises. 

Figure 2 illustrates a simple 3-choice olfactome¬ 
ter design used in initial olfactory training on a rel¬ 
atively pure primary vapor sample. Three gas sam¬ 
ple bottles are prepared. One contains a few ml of 
the primary odor sample; the remaining two con¬ 
tain negative control samples. Nitrogen gas, at the 
rate of 10 cc/min. is metered through each one of 
the three sample bottles and, ultimately, through 
three separate teflon tubings which are connected 
to stainless steel or Buchner funnels. The emission 
of the nitrogen gas odor carrier is then presented 
in the test odor ports for the dog to sample. When 
the dog responds to the primary odor at the cor¬ 
rect odor port, its behavior is reinforced with 
food. The odor ports are randomly changed after 
each trial to confirm that the dog is not position 
learning and to encourage it to sample all of the 
test odor ports. 

Table 1 is a sample data sheet used to record the 


453 


Restart 

<1 

i 

,Sniff -- Miss-- l ->Return to more basic olfactory training 

s 

/ 

s 

Sear ch-->Snif f-Detection-> Sit-> Good-> Food 

' (olfactory (conditioned (verbal (positive 

\ stimulus) reflex ) reinforcement) reinforcement) 

\ 

\ 

Sniff-False Sit-> Correct---> Kennel 1/4 to 6 hours 


NO! 


•"-> Examine apparatus for contamination 


Restart <-> Return to more basic training 

Figure 1. Correction of Alternate Behavior in Beginning Olfactory Training. 


dog’s progress during olfactory training. The trial 
number indicates the number of searches for the 
primary odor. Position number is the location of 
the primary odor with respect to the two control 
odors. The need for the position number is to ac¬ 
count for the frequent funnel changes in location 
during the exercise. The designated S +, S - , S - 
columns maintain a record of the olfactory sam¬ 
plings at each location. 

Usually, a learning exercise comprises 25 trials. 
Ideally the dog should sample the three odor ports 
or, in a more mechanical sense, take 75 sniffs of 
which 25 represent the primary odor. Except in a 
six-choice configuration where two primary odor 


samples are placed, the dog starts a new trial after 
finding the primary odor. A zero is used to record 
the fact that the dog did not place its nose in the 
odor port or otherwise did not sample. A negative 
sign in the score columns indicates that the dog 
sampled the odor effluent but did not respond 
which demonstrates odor discrimination. A posi¬ 
tive sign indicates the dog’s recognition of the 
odor by sitting at the primary odor port. A posi¬ 
tive sign recorded in a S - column is a false sit. An 
excessive number of false responses (5%) indicates 
that the apparatus is contaminated, faulty prep¬ 
aration of material, the dog cannot discriminate 
the primary odor, presences of a behavioral prob- 


Tablc 1. ABRIDGED SAMPLE OF OLFACTORY PROGRESS SHEET 

Primary Odor Sample EGDN Nitrogen Gas 

Control Odor Sample Distilled Water Nitrogen gas Date _Time 


Concentration 

10-6 

Dog 



Gas Flow Rate 

N lOcc/min 

Handler 



Trial 

Position 


Responses 


No. 

S + 

S + 

S- 

S- 


Primary Odor, 

EGDN + N 

Distilled H 2 0 

N 


e.g., Explosive 


+ N 



Heroin, etc. 




1 

2 

+ 

- 

0 

2 

1 

+ 

0 

0 

3 

1 

+ 

0 

0 

4 

3 

+ 

- 

— 

5 

2 

0 

- 

+ 

6 

3 

+ 

- 

- 

7 

1 

+ 

0 

- 

8 

3 

+ 

- 

— 

9 

2 

+ 

- 

0 

10 

2 

+ 

0 

— 

25 





Symbol 





+ 

Accurate Response 

9 



+ 

False Response 



1 

0 

Did Not Sample 

1 

4 

4 

- 

Discriminated 


6 

5 

— 

Did Not Respond 
to Primary Odor 





454 










PER 

MIN. 

Figure 2. Three-Choice Training Olfactometer. 

lem in the dog or poor trainer/handler perfor¬ 
mance. 

During the olfactory sensitivity and discrimina¬ 
tion training, approximately 12% of the dogs fail 
to progress. Failure results mostly from unsatis¬ 
factory behavior. 

Environmental task training, to some extent, is 
conducted in parallel with laboratory olfactory 
training. When the dog is performing near 100% 
in the laboratory odor detection, field training is 
emphasized. Field training requires the bulk of the 
500 hours; but, once each week, the dog is re¬ 
turned to the laboratory olfactometer for evalua¬ 
tion and reinforcement on the primary odor. Field 
training requires infinite patience by the trainer, 
consistent repetition of procedures in different en¬ 
vironments (depending on the ultimate task) and 
application of timeliness. 

In our work at SwRI, olfactory sensitivity tests 
for dynamite were conducted with experienced 
laboratory dogs. It was of interest to determine 
the highest dilution of a volatile substance in 
dynamite that would elicit a trained response in 
the olfactory dogs. In our early work, an assump¬ 
tion was made that repeated olfactory exposure to 
dynamite samples eventually would accustom the 
dogs to respond to an odor profile (a combination 
of vapors from the ingredients in dynamite) and 
not to a simple vapor stimulus. For the purpose of 
the detector dog study, an odor profile considered 
the following materials: nitrate of soda, ammoni¬ 
um nitrate, wood pulp, sulphur, wood flour, 
chalk and nitroglycerin (40% extra dynamite). 
Juhasz et al. (1973). However, the results of these 
experiments showed that a dog can learn to distin¬ 
guish by olfaction one or two volatiles in a spec¬ 
trum of volatile components. For example, it was 


suspected that nitroglycerine was the principal ol¬ 
factory stimulant in a dynamite odor profile that 
caused the dogs to make a positive response upon 
olfactory sampling. At that time, there was no evi¬ 
dence to indicate that ethylene glycol dinitrate 
(EGDN) was a major vapor component of dyna¬ 
mite. In a chemical analysis at the U.S. Army Bal¬ 
listic Laboratory of trapped vapors from five dif¬ 
ferent dynamite samples (100% blasting gelatin, 
40% extra dynamite, 60% extra dynamite, ditch¬ 
ing dynamite, 60% extra gelatin), ethylene glycol 
dinitrate was found to be the primary peak in the 
chromatograms of the volatile components. Chro¬ 
matographic analysis of the dynamite extract also 
confirmed the presences of EGDN as well as the 
nitroglycerine. On a chromatographic scan, at a 
flow rate of 0.8 ml/min, EGDN emerged in 6 min¬ 
utes and nitroglycerine at 8.5 min. Juhasz et al. 
(1973) 

In a series of olfactory test, the trained dyna¬ 
mite olfactory detector dogs responded to both 
volatiles, nitroglycerine and EGDN. The differ¬ 
ence in the manner of response to the EGDN sam¬ 
ple and nitroglycerine sample suggested with a 
high degree of certainty that the former sample 
was the primary odor stimulant. Since a pure sam¬ 
ple of nitroglycerine was unavailable, fresh medi¬ 
cinal nitroglycerine prells (used in patients with 
angina pectoris) containing .01 gr. nitroglycerine 
were used to test the response of the detector dogs 
upon their sampling of the vapor effluent. Three 
of the dogs had obvious delayed responses after 
sampling the prells. The fourth dog did not re¬ 
spond on the first two or three olfactory trials. On 
the other hand, each of the four dogs immediately 
responded to the EGDN sample. The results of 
these tests did not eliminate the probability that 
nitroglycerine was a part of the dynamite odor 
profile that stimulated the dogs to respond but, 
rather, demonstrated that EGDN was the primary 
olfactory stimulant. If EGDN had been absent in 
dynamite, then it is reasonable to assume that ni¬ 
troglycerine would have been the principal odor 
stimulant. 

It was not surprising to learn that EGDN was 
more volatile than nitroglycerine because of the 
difference in vapor pressure. Table 2 is reported to 
show the differences between the two volatiles at 
scaled temperatures. AMC Pamphlet (1971) 

An olfactory experiment was designed to test 
the dog’s olfactory sensitiveness to EGDN by dis¬ 
solving approximately 7.0 gms. to a one-liter vol¬ 
ume of warm distilled water. The molecular 


455 























Table 2. RELATIONSHIP TO VAPOR PRESSURES TO INCREXSE IN TEMPERATURE FOR EGDN ANI) 


NITROGLYCERINE 

EGDN 


mmHg °C 


.038 20 

0.26 40 

1.3 60 

5.9 80 


weight of EGDN is 152 gms; therefore, 1 ml vol¬ 
ume of solution would represent 4.6 x 10“ 5 M/1. 
Hence, a 1 ml aliquot of the initial solution deliv¬ 
ered to a volume of 1 liter would yield 4.6 x 10~ 8 
M per ml . . . 4.6 x 10“ 17 M. A 1 ml sample of the 
represented dilutions was added to a gas diffusion 
bottle that had a 10 ml/minute nitrogen gas flow. 
The exhaust flow was delivered through .079 cm 
Teflon tube to the olfactory sampling funnel for 
the experienced dogs to sniff. Four trained detec¬ 
tor dogs were used in the experiment. The experi¬ 
ment was designed to use a three-choice olfacto¬ 
meter. The two negative control sample bottles 
were adjusted to an equal nitrogen gas flow rate of 
10 ml/min. The negative control bottles contained 
1 ml of only distilled water. 

Each of the odor sampling ports were at nega¬ 
tive pressure so that the sample odor effluent was 
exhausted to the outside. To prevent room con¬ 
tamination with EGDN, the odor funnels were 
randomly relocated after one or two trials. The 
normal or pretest rate of detection efficiency on 
the dynamite samples was 94% to 99%. There¬ 
fore, when the rate of detection efficiency signifi¬ 
cantly declined during the trials, it was presumed 
that the dog’s olfactory sensitiveness to EGDN at 
that dilution level had also declined. During the 
olfactory experiments, each dog, during independ¬ 
ent trials, was released to commence its search at 
the olfactometer. If the animal made the correct 
response, i.e., sat at the sample odor port, it was 
positively reinforced. If the dog responded to a 
negative odor port, it was corrected and scored a 
false response. If the dog sampled the positive 
odor port and did not respond at any time during 
a two-pass search, it was counted as a miss but not 
as an incorrect response. Each test consisted of 25 
trials per dog. 

On the average, the results of these laborous 
tests indicated that the dogs, for the most part, 
were insensitive to EGDN at dilutions beyond 
10“ ,J M. Detection or performance efficiency aver¬ 
aged 85% at dilutions beyond 10“ 14 M. One dog 
sustained a 98% efficiency rate at 10“‘ M, but 


Nitroglycerine 

mmHg °C 


.00025 

20 

.0024 

40 

.0188 

60 

.098 

80 


gave no indication that it could detect EDGN va¬ 
pors at 10“ 19 M. 

An additional experiment with EGDN was con¬ 
ducted at sub-zero temperatures; i.e., the samples 
and gas and vapor tubing were at -30°C. These 
trials were preliminary to transporting dogs from 
San Antonio to Colorado for the purpose of ex¬ 
plosive detection studies in snow and freezing 
temperatures. Undiluted EGDN samples at sub¬ 
zero temperatures in the laboratory presented no 
difficulty for the EGDN olfactory sensitive dogs. 

An epilog to these studies is that the test dog, 
never having been in snow or sub-zero weather, 
uneventfully adapted to the environment and, 
without apparent difficulty, located 96% of the 
buried surrogate mines containing dynamite and 
TNT. When a dog was unresponsive at a mine site, 
it was because the vapors were not available to 
sample. The mine samples were emplaced six 
hours before testing. 

A translated version of a Russian report further 
documents the olfactory acuity of dogs in terms of 
olfactory threshold. Pavlov (1958), Myznikev The 
literature cites enhanced olfactory sensitivity of 
service dogs administered either caffine or am¬ 
phetamine one hour post-ingestion. Olfactory en¬ 
hancement persisted for eight hours. Continuous 
or repeated use of amphetamine markedly reduced 
the test dog’s olfactory capabilities. Bromide used 
with amphetamine appeared to balance the proc¬ 
ess of inhibition and excitation in otherwise excit¬ 
able or apprehensive dogs. Dogs were dosed for 
7-10 days. The primary or test odors used in the 
olfactory threshold tests, as described in the re¬ 
port, were serial dilutions of thymol, acetic acid 
and ammonia in distilled water. 

The results of this experiment showed an in¬ 
creased olfactory threshold value by two to three 
orders of magnitude over the pre-dose threshold 
value. For example, in one dog, the pre-dose 
threshold value for ammonia was 10' 10 dilution 
and, after administration of caffine, the threshold 
value was 10“ 13 . Doses of amphetamine did not in¬ 
crease the threshold value beyond that which was 


456 



achieved by caffine. In another dog, the caffine 
pre-dose threshold of 10~ 17 for ammonia in¬ 
creased to a value of 10“ 19 dilution. The latter test 
showed that not only did caffine improve olfac¬ 
tory acuity in the test dog but demonstrated that 
there are differences in olfactory sensitiveness 
among dogs of the same breed. Two of the dogs in 
the experiment demonstrated pre-dose values on 
the order of 10" 24 . The pre-dose and post-dose 
threshold values for each experimental dog were 
generally consistent with ammonia, acetic acid 
and thymal dilutions. 

The methods used at SwRI for developing olfac¬ 
tory detector dogs have produced dogs of lasting 
qualities. One dog frequently used in laboratory 
procedures is 12 years old and, except for slow¬ 
ness, shows only a minor decline in performance. 
It has been repeatedly demonstrated that dogs can 
detect a primary odor and individually work, de¬ 
pending on training, in an assortment of task en¬ 
vironments. Some of the primary odors we have 
successfully worked with have been TNT, dyna¬ 
mite, plastic explosives, smokeless gun powder, 
black gunpowder, Heroin Hcl, and many other 
narcotics, personnel odor markers, dielectric cable 
oil, Black Footed Ferret scent and human scent. It 
might be noteworthy to expand these feasibility 
studies to include paired odors, for example, guns 
and emotionally distraught persons or even the 
odor effluent of radiation sickness. If dogs are to 
be used in a legal sense, research studies should be 
conducted to establish evaluation criteria for dog 
and handler that will eventually lead to bi-annual 
certification. Through very explicit training and 
repetition, a good dog can be made a successful 
and dependable olfactory detector. 

The foundation for developing detector dogs is 
based on positive reinforcement of desired be¬ 
havior with systematic verbal and food reward. 
Timeliness, consistency and repetition is of es¬ 
sence. One must remember the basic feature on 
which sound training can begin—the alimentary 
reflex is one of the strongest reflexes inborn in the 
animal. In fact, one of the important criteria for 
selection of dogs is an overt display of a healthy 
appetite. The Clever Hans phenomenon (cues) 


must be a primary concern during training and 
during work. Hedigu (1981) Although it can never 
be totally achieved, it is best to develop the detec¬ 
tor dog to be as independent as possible of direct 
handling. 

REFERENCE 

AMC Pamphlet 706-177 (1971). Explosives Series 
Properties of Explosives of Military Interest. 
Hq., U.S. Army Material Command. 

Dean, E. E. (1973-1975). Proceedings 1975 
Carnahan Conference on Crime Countermeas¬ 
ures. UKY BU 107:141-144. 

Dukes, H. H. (1955). The Physiology of Domestic 
Animals, 7th Ed. Comstock Publishing Asso¬ 
ciates, Ithaca, New York. 

Hediger, H. K. P. (1981). The Clever Hans Phe¬ 
nomenon From an Animal Psychologist’s Point 
of View. The Clever Hans Phenomenon: Com¬ 
munication with horses, whales, apes and peo¬ 
ple. Editors: Sebeok, T. A., Rosanthal, R., 
Annals of The New York Academy of Sci. 
364:1-17. 

Juhaz, A. A., Doali, J. O., Rocchio, J. J. (1973). 
Examination of Vapors From Commercial 
Dynamite. Interim Memorandum Report No. 
92, USA Ballistic Research Laboratories, Aber¬ 
deen Proving Ground, Maryland. 

Moulton, D. G. (1976). Enhancement of Olfac¬ 
tory Discrimination. Final Report, Grant No. 
AFOSR. 73-2425. 1-2. 

Myznikev, N. M. (1953). The Sensitiveness of ol¬ 
factory analyzer of service dogs and the meth¬ 
ods for their augmentation. Bio/No. 3529. 
From Committee for Scientific Actions of Na¬ 
tional Defense Center, etc. 

Pavlov, I. P. (1958). Journal of the Higher Ner¬ 
vous System, Moscow 8, No. 5: 744-750. From 
Committee for Scientific Actions of National 
Defense Center of Exploitation of Scientific and 
Technical Information. 

Phillips, R., Dean, E. (1973-1975). Proceedings 
1975 Carnahan Conference on Crime Counter¬ 
measures. 

Wright, R. H. (1982). The Sense of Smell. CRC 
Press. Inc., Boca Raton, Florida, 107-113. 


457 






















• 





INDICATOR TUBES FOR THE DETECTION OF TNT 


Eric D. Erickson, Sterling R. Greni, Daniel J. Burdick 
and David J. Knight 


ABSTRACT. A field detector kit for trinitrotoluene (TNT) in water has been de¬ 
veloped at the Naval Weapons Center. In addition, a simple extraction technique 
has been developed which permits the use of this kit to detect TNT in soil. This kit 
has been developed in order to assist munitions manufacturers and regulatory or¬ 
ganizations in their pollution abatement efforts. Forensic applications are also en¬ 
visioned when it is necessary to determine if ordnance used to commit a crime con¬ 
tained TNT. The operation of this detector kit involves passing an aqueous solu¬ 
tion of TNT through a bisectional indicator tube. The basic oxide pretreatment 
section of the tube converts the TNT to its Meisenheimer anion. The indicator sec¬ 
tion of the tube contains an alkyl quaternary ammonium chloride anion exchange 
resin which traps the colored anions, forming a stain whose length is proportional 
to the flow rate, volume, and concentation of the TNT solution. Indicator tubes 
have been developed for use in two different concentation ranges. The first tube is 
useful in the 0.1-10.0 ppm range while a low concentration tube is useful in the 
10-200 ppb range. 


Munitions manufacturers and environmental 
regulatory agencies need to monitor toxic explo¬ 
sives and their byproducts left in effluent from the 
manufacturing processes. Also, after an explosive 
has been used to commit a crime, forensic experts 
need to identify the explosive from residues in wa¬ 
ter, soil, or air. A method is needed to provide 
rapid analysis in the field. This paper describes a 
method for the analysis of trinitrotoluene (TNT) 
in water (Heller et al. (1982) and Greni and Erick¬ 
son (1982)). The work described was performed as 
part of the Pollution Abatement Program at the 
Naval Weapons Center and was funded under 
Program Element Number 62765N, NAVSEA 
Task Area Number SF65572391 under sponsor¬ 
ship of Dr. George Young and under 
USATHAMA Task Numbers R904.10.0263 and 
P13 under sponsorship of Captain Peter Rissell. 

Before deciding which method could best be 
adapted to use as a field detector, it was necessary 
to draft a list of criteria which must be met by any 
field detector. The detector needs to be portable to 
permit it to be brought to the sample. The time re¬ 
quired to perform the analysis should be of short 
duration, preferably less than 10 minutes. Many 
applications have limited quantities of the sample 
available for analysis, therefore the method 
should require small sample volumes. Species 


which can generally be expected to be present in 
the sample should not interfere with the analysis. 
Minimum technical training should be necessary 
to operate the detector, and the technique should 
not present a health hazard to the operator. 

Currently, a wide variety of analytical tech¬ 
niques are available for the detection of TNT in 
water. These include oxidation of the solution fol¬ 
lowed by a colorimetric determination of the ni¬ 
trate content (Leggett (1977)); extraction of the 
TNT into an organic phase which is then subjected 
to a gas chromatographic analysis; reverse-phase 
high performance liquid chromatographic tech¬ 
niques; electrochemical techniques; and a method 
in which one monitors the fluorescence quenching 
of TNT trapped on a fluorescent ion exchange res¬ 
in (Heller et al. (1977)). Few of these techniques 
can be considered portable as they usually require 
samples to be collected and sent to a lab for analy¬ 
sis. These methods generally require the operator 
to have extensive chemical training in order to per¬ 
form the analysis, and they can all present health 
hazards to the analyst. 

Therefore, we decided to scrap these techniques 
as possible field methods and look for other possi¬ 
bilities. Health science specialists have used indi¬ 
cator tubes for years to obtain a rapid approxima¬ 
tion of the concentration of contaminants in the 


459 


air. Such a technique meets our criteria for a field 
detector. 

We have developed an indicator tube for the de¬ 
tection of TNT in water which is based on the for¬ 
mation and subsequent collection of the red Mei- 
senheimer anion. The Meisenheimer anion is 
formed by treating the TNT with hydroxide ion. 
The resulting anion is trapped onto a strongly bas¬ 
ic anion exchange resin. 

The indicator tubes which we have developed 
are prepared from 4 mm inner diameter (6 mm 
outer diameter) glass tubing which has a length of 
12 cm. These tubes are packed in two sections 
which are separated and held in place with glass 
wool plugs. The first or presection consists of 
glass beads which have been coated with a mixture 
of calcium, magnesium, and barium oxides. It is 
in this section that the TNT Meisenheimer is 
formed. The second or indicator section consists 
of a quaternary ammonium chloride anion ex¬ 
change resin. While any strongly basic anion ex¬ 
change resin will trap the colored TNT anion, 
many of those available commercially are not ade¬ 
quate for this method since the hydroxide form of 
these resins is red. We have been using AGMP-1 
resin (manufactured by Bio-Rad). This resin is 
beige in both the chloride and hydroxide forms. 

Upon contact with the ion exchange resin, the 
TNT Meisenheimer anion is trapped forming a red 
stain (the length is proportional to the solution 
volume, the flow rate, and the solution concentra¬ 
tion). By holding the first two variables constant 
at 10 ml and 2.7 ml/min, respectively, we are able 
to use this indicator tube to detect concentrations 
from 0.1 to 10 ppm TNT in water. 

A second indicator tube has been developed to 
monitor smaller concentrations. This tube uses 1.7 
mm inner diameter (7.0 mm outer diameter) capil¬ 
lary glass tubing packed with the same compo¬ 
nents as the other tube. Using a flow rate of 1.0 
ml/min and a 10 ml volume, this tube can be used 
to detect concentrations between 20 and 200 ppb. 
Increasing the volume of the sample would enable 
the analyst to detect even smaller concentrations. 

We have designed a kit to enable us to use these 
indicator tubes in the field. This kit consists of 
several indicator tubes, a 10 ml syringe, a 
Swage-lok/Luer-lok coupler, a syringe pump, 
and a bottle of 1.0 ppm TNT standard. These 
components are stored in a briefcase for conveni¬ 
ence in transporting to the site. For those occa¬ 
sions when electrical power is not available to op¬ 
erate the syringe pump, we also include a power 


inverter which can operate from a car battery. 

In order to use this kit, the syringe is loaded 
with the sample and connected to the luer side of 
the coupler. An indicator tube is connected to the 
swage side of the connector. This apparatus is 
then placed on the syringe pump and the proper 
flow rate is selected. Concentrations are deter¬ 
mined by comparison of the stain length with that 
similarly obtained using TNT standards. 

A technique has been developed to use these in¬ 
dicator tubes to determine the TNT content of 
soil. An aliquot of soil is extracted with an ace- 
tone:water mixture. The resulting solution is then 
filtered and passed through the tube as if it were a 
water sample. 

While we have not attempted the analysis, it is 
conceivable that these indicator tubes could also 
be used to monitor TNT vapor in air. An impinger 
technique could be used to collect an aqueous 
sample for passing through the indicator tubes. 
Alternatively, a more direct determination may be 
possible using tubes containing anion exchange 
resin which has been wet with a sodium hydroxide 
solution. This would cause the in situ formation 
and collection of the TNT Meisenheimer anion. 
These techniques need to be examined in the fu¬ 
ture. 

Interference studies have been performed using 
these tubes, stressing the priority pollutants and 
other explosives. These studies were conducted to 
determine if the specie of interest stained the resin, 
reacted with hydroxide to form a compound 
which would stain the resin, or altered the stain 
length expected from a TNT standard solution. 
Several interfering species have been identified. A 
pH below 6.5 prevents the formation of the TNT 
Meisenheimer anion. Above a concentration of 
2.0 ppm, 2,4-dinitrotoluene produces a green 
stain on the resin. 2-Amino-4,6-dinitrotoluene al¬ 
so produces a green stain on the resin in concen¬ 
trations above 10 ppm. These two compounds 
seem to undergo some sort of chemical reaction 
with the resin other than an ion exchange reaction. 
Without the pretreatment section in place, ion ex¬ 
change reactions occur to form yellow stains from 
3,5-dinitro-o-cresol and 4,6-dinitro-o-cresol 
above concentrations of 100 and 40 ppb, respec¬ 
tively. Red stains are formed in the presence of the 
presection from 2,4-dinitroanaline and tetryl 
above concentrations of 0.2 and 0.5 ppm respec¬ 
tively. Except for differing shades of red, these 
two compounds can not be identified as different 
from TNT using this method. 


460 


Currently, there is no simple mathematical ap¬ 
proximation for determining the concentration of 
a solution directly from its stain length. We be¬ 
lieve that this is due to the porosity of the resins 
which we have been using. With these resins, the 
TNT Meisenheimer is able to migrate to exchange 
sites within the resin pores, resulting in a stain that 
is darker at the front end of the indicator section 
than further down the tube. This problem could 
be corrected using a pellicular resin. Advantages 
of a pellicular resin should be an increase in the 
stain length, sensitivity, and the linearity of the 
technique. Disadvantages are that the stain would 
be lighter due to the decreased number of ex¬ 
change sites available on the resin, the resin is not 
commercially available in a useful size range, and 
these resins are difficult to prepare. Attempts have 
been made to prepare pellicular resins in the lab by 
coating inert surfaces with powdered porous res¬ 
ins. Uniform coatings have not yet been achieved, 
but preliminary data suggest that our assumptions 
are correct and pellicular resins should solve some 
of our problems. 

The TNT indicator tube kits meet our require¬ 
ments for a field detector. Future work will be di¬ 


rected towards improving the linearity of the tech¬ 
nique. In addition, we plan to develop indicator 
tubes for the detection of ammonium picrate, tet- 
ryl, 2-amino-4,6-dinitrotoluene, nitroglycerine, 
nitrocellulose, propylene glycol dinitrate, HMX, 
RDX, and other explosives of military interest 
found in water. 

REFERENCES 

Greni, S. R. and Erickson, E. D. (1982). Anion 
exchange resins for the detection of 2,4,6-trini¬ 
trotoluene in water. NWC TP 6357, Naval 
Weapons Center, China Lake, Calif. 

Heller, C. H., Greni, S. R., and Erickson, E. D. 
(1982). Field detection of 2,4,6-trinitrotoluene 
in water by ion-exchange resins. Anal. Chem. 
Vol. 54, No. 2:286-289. 

Heller, C. H., McBride, W. R., and Ronning, 
M. A. (1977). Detection of trinitrotoluene in 
water by fluorescent ion-exchange resins, Anal. 
Chem. 49:2251. 

Leggett, D. C. (1977). Determination of 
2,4,6-trinitrotoluene in water by conversion to 
nitrate. Anal. Chem. 49:880. 


461 


















THE TAGGING OF EXPLOSIVES; 

THE NEW SWISS LAW ON EXPLOSIVES: 
DEVELOPMENT, ACHIEVEMENTS AND FIRST EXPERIENCES 


Jurg Scharer 

Chief Analytical Department 
Zeughausstr. 11, 8004 Zurich 
Switzerland 


ABSTRACT. In Switzerland the marking of explosives, safety fuses, detonating 
cords and fusetubes is embodied in law. This act and its administrative rules are 
herewith presented, completed by the description of the present day situation in 
Switzerland, the applied investigation procedures for bombings, the efforts taken 
so far (details on the two systems “MICROTAGGANT” and “EXPLO- 
TRACER”) and future developments. 


Organization and Function of the Institute of For¬ 
ensic Science (IFS) 

The Institute of Forensic Science represents a 
small department consisting of five associates of 
the Scientific Service, in charge of criminal investi¬ 
gation, of the city police of Zurich. It is directly 
controlled by the Federal Attorney. Its functions 
are, among others, to investigate all crimes where 
explosives are involved all over Switzerland. This 
includes: 

1. The recovery of debris as a result of a bomb¬ 
ing on the spot 

2. The analysis of all the recovered debris in 
our laboratories 

3. The neutralizing of improvised blasting and 
incendiary devices (EOD) 

4. The instruction and training of all Swiss po¬ 
lice corps of the caution to be observed while 
using explosives in dealing with terrorist 
bombings 


5. The working out of expert’s reports for the 
judicial authorities. 

However, it is new for the Institute of Forensic 
Science to function as the central authority regard¬ 
ing the Swiss Act on explosives. 

In this context, we are among other things the 
authority for—the examination and elaboration 
of new tagging systems of explosives. 

The Origin and Implementation of the Act on Ex¬ 
plosives 

The Swiss Act on explosives and its administra¬ 
tive rules were put into force on July 1, 1980. The 
transitional regulations and some prolongations 
of term led to the fact that the regulations of tag¬ 
ging, in particular, could only have been fully ap¬ 
plied since January 1, 1983. This is why we don’t 
have a wide range of experience in the effects of 
these regulations at this time. The tagging of ci¬ 
vilian explosives became a part of the law in 


THE COMPOSITION OF SEVERAL GELATINE EXPLOSIVES 
IN % (APPROXIMATELY) 



Switzerland 


Federal Republic 

Italy 




of Germany 



Gamsite A 

TelsitA 

Ammongelit I 

Sismic I 

Nitroglycol 

25 

25 

38 

25 

DNT/TNT (Isomers) 

6 

8 

4 

9 

Nitrocellulose 

1 

1 

2 

1 

Ammoniumnitrate 

61 

61 

52 

60 

Wooddust 

4 

2 

4 

1 

Baricsulphate 

3 

3 

— 

4 

Ferric oxide 

0,5 

0,5 

0,2 

— 

Inert (indeterminable) 

— 

— 

— 

0.5 


463 


Switzerland as a result of the fact that: 

—the explosives used for criminal purposes in 
Switzerland were obtained from more than 
90% of civilian sources (refer to Figures 1,2) 
—practice has shown that in many cases an 
analysis of the residual of exploded devices is 
unsuccessful (e.g ., extremely contaminated 
traces, or traces made useless because of envi¬ 
ronmental causes, such as water, fire, etc.) 

—and, even when the proper testing procedure 
is employed with such explosive components 
as PETN, DNT, nitroglycol, ammonia ni¬ 
trate, etc., the specific origin still cannot be 
determined. As the following table shows, the 
chemical composition of various explosives 
can be similar in one country and likewise, it 
can be similar in different countries. 

The Provisions of the Act Concerning the Tagging 
of Explosives and their Practical Application 

Article 5, Section 3 of the administrative rules 
on explosives says: 

“All explosives must contain a specimen substance by 
which its origin can be definitely traced, even after the 
explosive has been detonated. This substance used by 
the manufacterer for the marking of explosives is sub¬ 
ject to a permit, issued by the coordinating office of 
the Federal Attorney.” 

Origin is referring to the place of production. In 
Switzerland, there are four manufacturers and 
two importers of explosives. According to the 
legal text, six different marking substances (codes) 
would be enough. 

Even though, in conforming with the legal text, 
one marking substance or code per manufacterer 
would be sufficient, we agreed with the manufac¬ 
turers of tagging substances to automatically send 
a new code with every new lot. And, in addition to 
this, we could persuade the manufacturers and im¬ 
porters of explosives to use different codes for 
some different products. 

By the end of 1982, there were 32 different ex¬ 
plosives in Switzerland which were tagged with 22 
different codes. The total amount of the tagged 
explosives is between 11 and 50 U.S. tons. As early 
as the beginning of 1979, we had a meeting with 
the Swiss manufactuers of explosives. On that oc¬ 
casion we presented the “3M”-MICROTAG- 
GANTS, which was at that time only existing tag¬ 
ging-system for explosives. We informed the 
manufacturers at that meeting, that we would ap¬ 
prove this in the USA developed tagging-system. 
Exactly two months before the fixed deadline on 
which the obligation of marking would be put into 
force, we received from the “Societe Suisse des 


Explosifs S.A.,” a manufacturer of explosives in 
the canton of Valais (Switzerland), 50 pounds of 
the explosive TOVEX A, a water gelatin explosive 
containing a newly developed tagging substance 
called EXPLOTRACER. 

Even though many of you are familiar with the 
tagging-substance developed by “3M”, I would 
like for the sake of completeness to briefly present 
to you the two substances which have been ap¬ 
proved so far in Switzerland. 

The so-called MICROTAGGANT—the pro¬ 
duce of “3M CO.”, St. Paul, Minnesota/USA— 
consists of multilayered melamine resin lamina 
with a maximum diameter of 800 ^m (Figure 3). 
Nine coloured layers represent the code. These 
layers are recognizable at a magnification rate of 
40 to 100. With these nine layers it is possible to 
create several hundredthousand combinations or 
codes. One side of the layer. This enormously fa¬ 
cilitates the finding of the particles as well as those 
in the explosive itself during the recovery. A fur¬ 
ther lead to recovery and subsequent identification 
is provided by a magnetic susceptible layer (0 = 
black). This feature allows for the collection of 
taggants by use of magnets. Because of the high 
production costs of the tagging substances (it is 
being produced exclusively for Switzerland) we 
obtained approval of an absolute minimal quota 
of 0,025% within the explosive itself. 

The tagging substance EXPLOTRACER from 
the ‘‘Societe Suisse des Explosifs,” Gamsen, was 
developed and produced by the ‘‘Plast Laborato¬ 
ries,” Bulle/FR, Switzerland (Figure 4). This tag- 
gant is based on coloured plastic powder mixed 
with flourescent pigments. In order to obtain mag¬ 
netic susceptible particles, the basic material was 
mixed with iron powder. Rare-earth elements and 
other additional substances (inorganic com¬ 
pounds, such as, oxides, etc.), allow for the analy¬ 
tical verification. Thus, it was possible to provide 
this substance with the same qualities as the ‘‘3M” 
tagging system, especially with respect to recovery 
and preservation of the particles. 

The taggant can be easily detected with the aid 
of a long-wave ultra-violet light source and can be 
additionally separated by using magnets to sepa¬ 
rate from non-magnetic susceptible materials. 
This EXPLOTRACER is a granulate with grains 
from 200 to 800 which is to be mixed with the 
explosives at the rate of 0,1%. The various com¬ 
ponents of this substance: the polymer, the flour¬ 
escent pigment and the rare-earth elements and 
additional substances, provide the code composi- 


464 


THE IFS INVESTIGATION OF BOMBING AND 
BOMBING ATTEMPTS IN SWITZERLAND 
DURING 1979 - 1981 


NUMBER 
20 : - 


15 
10 

5 + 


22 , 0 % 


39,0% 


: mm 6 ' 0% * 78 ' 0% 

33,0% 


37,0% 

25,0% 

37,5% 


>62,5% 




1981 1980 

HI CIVILIAN SWITZERLAND 


11 CIVILIAN FOREIGN COUNTRIES 
I 1 CIVILIAN INDETERMINABLE 

Figure 1. 



19,0% 
5,0% 
5,0 %■ 

28,0% 


>71,0% 


43,0% 


1979 

SELF-MADE 

MILITARY 

EXPLOSIVE AMMUNITION 
INDETERMINABLE 


SAFE ROBBERIES WITH EXPLOSIVES IN SWITZERLAND 

DURING 1979 - 1981 


NUMBER 



fliim CIVILIAN SWITZERLAND 
liiiii CIVILIAN FOREIGN COUNTRIES 
I CIVILIAN INDETERMINABLE 


I MILITARY 
] INDETERMINABLE 


Figure 2. 


465 


































































































































































MICROTAGGANT 

developed by 3M Co., Minnesota / USA 


COLOUR -code"! 





F 342861930 


1 



Figure 3. 


EXPLOTRACER 

developed by PL AST LABORATORY CO., Bulle / Switzerland 


CODE 

THOUSAND 

HUNDRED 

Z 

UJ 

t— 

1— 

z 

=) 

Basic Polimer 

1 




Fluorescent Pigment 


2 



Rare-Earth Elements 



4 


Additinal Substances 




T 



Figure 4. 


tion. If there are ten forms available from every 
component, there would be a result of almost 
10,000 combination possibilities. 

The enormous advantage of this system consists 
of the easy detection of the particles after the ex¬ 
plosion. This is due, on one hand, to the relatively 
large quantity of taggants (0,1 %) and on the other 
hand, to their being completely flourescent. Their 
magnetic susceptibility turns out to be less than 
with the “3M” product because the iron particles 
mix irregularly with the granulate. 

In addition to this, the fact is, that the amount 
of time necessary to verify and decode these parti¬ 
cles is relatively high because they need intensive 
physical-chemical examination. 

The following methods are used to analyze the 
different components: 

(a) Plastic powder. The plastic powders used 
so far may be differentiated by their melting 


466 
























































































































































points by a thermal analysis or under the po¬ 
larization microscope. 

(b) Flourescent pigments. With about five tag- 
gants it is possible to produce a thin layer al¬ 
lowing the spectral analyses of the fluorescent 
pigments within ultra-violet or visual percep¬ 
tibility of 300 to 600 nm. 

(c) Rare-earth elements and additional sub¬ 
stances. With the aid of an X-ray spectrom¬ 
eter it is possible to analyze rare-earth ele¬ 
ments and additional substances (inorganic 
elements) already with the presence of one 
single particle. 

While this paper was being written, we received 
a third tagging substance, manufactured by the 
Haniel Blasting Co., Switzerland. This taggant is 
not yet fully developed but is similar to the “3M” 
product which is based on multilayered coloured 
particles. 

Now, let’s consider the practical aspect of the 
preservation of traces. As mentioned above, the 
so-far admitted taggants are based on fluorescent 
and magnetic susceptible layers. These two quali¬ 
ties, necessary for the analyses and preservation 
will be the basic requirements for all further possi¬ 
ble taggants. In the meantime, the following 
methods of preserving traces are useful: 

Procedure A: 

—Collection of single taggants after detecting 
them with ultra-violet light by means of 
tweezers, spatula, pointed spoon or magnetic 
needle. 

This method requires almost entire darkness 
and is very tiring, especially for the eyes. So far, 
we have been working outside under blankets. 
Some first trials with boxes equipped with 
peep-hole and ultra-violet lamps were equally 
promising. 

Procedure B: 

—Systematic collection by use of magnets. 

For this procedure we use magnetic plates, a 
method already developed by ATF. The use of 
magnetic plates is an adequate procedure to swab 
an even surface. To begin, a magnet is placed in¬ 
side a plastic bag which is used to collect the mag¬ 
netic particles. To collect the particles, the bag is 
removed from the magnet by turning it “outside 
in.’’ In this way, the particles are gathered inside 
the bag. 

Procedure C: 

—Gathering the particles With the aid of 


brooms/brushes of different kinds on dry 
and even surfaces. 

This procedure proves to be inadequate as soon 
as the surface is damp. A further drawback results 
in the fact that the brooms are very difficult to 
clean after use. To prevent any dragging of tag¬ 
gants, it is best to use them only once. 

ProcedureD: 

—Wiping the particles off with cotton or cellu¬ 
lose. 

This procedure proves adequate for even, as 
well as damp surfaces. This method is well suited 
for preserving the explosive residues, as well as the 
taggants, in one procedure. In the first phase, the 
surface gets cleaned with cotton and acetone (de¬ 
tachment of the organic components of the explo¬ 
sive) and in a second phase, with cotton and water 
(detachment of the inorganic components. 
Procedure E: 

—Sucking off with a special vacuum cleaner. 

Our vacuum cleaners, developed for the preser¬ 
vations of microtraces, prove to be very useful in 
the preservation of taggants, too. By the means of 
a special filter element at the mouth of the vacuum 
tube or the application of our specially designed 
broom device, a total success may be guaranteed. 
The removal of the tiny substances in front of the 
filter is quite easy and can be controlled. 

Procedure F: 

—Printing off with adhesive tape. 

This procedure applied on dry, even surfaces 
brings excellent results. It is an adequate proce¬ 
dure for small areas in particular. For larger areas, 
however, this procedure is too complicated. It 
needs to be taken into consideration that any ex¬ 
plosive residues which stick to the tape, may later 
encounter difficulty, if not an impossibility, to be 
completely removed from the adhesive of the tape. 
The debris collected in one or another manner as 
described, is processed later in the laboratory with 
customary methods for organic and inorganic ex¬ 
plosive substances, such as, the nonexplosives resi¬ 
dues. 

Depending upon whether microtagging has been 
found in sufficient number, it is now necessary to 
proceed with an intensive searching for taggants. 
For that purpose, the entire collected material and 
filtrates will be placed by small portions into glass 
beakers with some water. By means of a magnetic 
stick, it will be stirred and the magnetic susceptible 
parts on the stick will be placed into a second glass 
beaker with water. By removing the magnetic stick 


467 


out of its tube, the particles will fall off. This pro¬ 
cedure is repeated until all magnetic susceptible 
particles are transferred. To separate the taggants 
from the often very numerous extraneous and in- 
terferring debris, the materials are transferred into 
another glass beaker by a further phase. This glass 
is filled with a solution of sufficient density in ac¬ 
cordance with John A. Kearn’s method, so that 
the taggants float. All of the other magnetic sus¬ 
ceptible particles do not float; they will sink to the 
bottom of the glass. With the aid of a long-wave 
ultra-violet lamp, the fluorescents will get acti¬ 
vated and the taggants can be separated. 


In our administratives rules there exist not only 
rules concerning the tagging of explosives, but 
also concerning the marking of the most frequent 
igniters and lighters. 

Article 7, Section 1 of the administrative rules 
on explosives provides the following: 

“Safety fuses and detonating cords, as well as fuse 
tubes, must contain a marker throughout their entire 
length, which identifies the manufacturer, place, year 
and month of manufacturer.” 

Safety fuses have been provided with special 
marking threads. Figure 5 shows an example of 
marking colors for the years 1981 to 1982. 



COLOUR-CODE 


NUMBER OF THE 
MARKING THREAD 


JEAR(2 THREADS) 

MONTH (1 THREAD) 

01 

BLACK 

■ 1981 

JANUARY 

02 

mn rmfTTi 111 n 111111111 

YELLOW 

1982 

FEBRUARY 

03 

GREEN 

■ 1983 

MARCH 

04 

RED 

11 1984 

APRIL 

05 

• ^ ' . «... . • .1, *r / ■ 

LIGHTBLUE gS§ 

H 1985 

MAY 

06 

YY/YYYYYYY^YY/YY/YYYYYYYYYYYYYYYYYyJ^^ 

ORANGE 

1 1986 

JUNE 

07 

GREY —- 

HI 1987 

JULY 

08 

PINK : 

PI 1988 

AUGUST 

09 



SEPTEMBER 

BLUE SH 

M 1989 

10 

YELLOW-GREEN 

1990 

OCTOBER 

11 

BROWN 

H 1991 

NOVEMBER 

12 

VIOLET ^ 

= 1992 

DECEMBER 


0204 = 1982 APRIL | 


Figure 5. 


468 










































































































Twelve marking-thread numbers were com¬ 
bined with 12 well defined colors. By bringing in 
two threads with the same color, the year is indi¬ 
cated, and with the third colored thread, the 
month is determined. 

The example shows two yellow threads indicat¬ 
ing the year of manufacture (1982) and the red 
thread, the month of manufacture (April). 

You may be struck by the fact that the marking 
threads indicating the date of manufacture are 
found immediately under the plastic coat. This is 
according to our requirements because marking 
threads around the core of the safety fuse cannot 
be analyzed after it has burned. 

The identification of both burned or unburned 
parts of safety fuses is possible by uncoiling the 
threads. To decompose the fuse, we put it into 
xylene. 

Explosive cords are partly provided with mark¬ 
ing threads, too. As this legal text does not deter¬ 
mine the kind of marking, different solutions 
might be proposed. Figure 6 shows that the mark¬ 
ings for the manufacturers have been chosen in 


various forms. Thus, for example, two products, 
such as one explosive cord (Detonex) and the 
safety fuse (Fritzsche), are marked by additional 
plastic coats in the cord in place of the colour 
threads to determine the place of manufacture. 

The third article, concerning the marking of ex¬ 
plosives, will be found in the administrative rules, 
Article 9, Section 1: 

“On all blasting caps (detonators), electric or non¬ 
electric, a marker shall be affixed which identifies the 
manufacturer, place, year and quarter of manufac¬ 
ture.” 

This article, the only one of all the rules is not 
effective up to the present day. The reason is, that 
in Switzerland there is no manufacturer of blast¬ 
ing caps. 

Practice shows, that detonators and blasting 
electric caps frequently are not totally inserted 
into the explosive (primarily safe-cracking with 
the help of explosives) and therefore their rear 
portion may not be completely destroyed. For this 
reason, we would like to have the rear portion of 
detonators provided with specific colours or, in 


MARKING OF DETONATING CORDS AND 
SAFETY FUSES IN SWITZERLAND 


(Situation Oct. 82, Art. 7 Sect.l, Administrative Rules on Explosives) 



PLACE OF MANUFACTURE 

MARKING FOR 

YEAR 

MONTH 

Detonating Cords 

DETONEX 

SOCI£t£ SUISSE DES 
EXPLOSIPS/ GAMSEN/CH 

PLASTIC WRAP 

RED-ORANGE 

1 COLOURED THREAD 

IN EXPLOSIVE CORE 

1 COLOURED THREAD 

IN WRAP 

DYNACORD 

DYNAMIT NOBEL AG 

TROISDORF/FRG 

1 MARKING-THREAD 

RED-VIOLET IN WRAP 

2 COLOURED THREADS 

IN WRAP 

1 COLOURED THREAD 

IN WRAP 

TITACORD 

SOCI£t£ DES EXPLOSIFS 
PONTAILLER S.S./F 

1 MARKING THREAD WHITE 

IN EXPLOSIVE CORE 

2 COLOURED THREADS 

IN EXPLOSIVE CORE 

1 COLOURED THREAD 

IN EXPLOSIVE CORE 

DETACORD 

DYNAMITE S.D.A- 
UDINE/I 

2 MARKING-THREADS 

RED AND WHITE IN 
EXPLOSIVE CORE 

2 COLOURED THREADS 

IN WRAP 

1 COLOURED THREAD 

IN WRAP 

Safety Fuses 

FRITZSCHE 

FRITZSCHE, MINUSIO/CH 

2 ADDITIONAL PLASTIC 

COATS IN CORD 

2 COLOURED THREADS 

IN WRAP 

1 COLOURED THREAD 

THREAD IN WRAP 


Figure 6. 


469 



















the case of blasting electric caps, with specifically 
pigmented stoppers. As I learned at the 
“3M”-Factory in St. Paul, a spray containing in¬ 
delible microtaggants is being currently tested. We 
will examine it further to see whether or not it is 
suitable for the marking of detonators and blast¬ 
ing electric caps. 

SUMMARY 

Finally I’d like to summarize the most impor¬ 
tant facts in connection with the new provisions: 

—The adapted marking provisions in the new 
act on explosives include all explosives serv¬ 
ing civilian purposes, as well as safety fuses 
and explosive cords and, within a reasonable 
period of time, detonators and blasting elec¬ 
tric caps. We are convinced that this complete 
tagging and marking system will strengthen 
and support the evidence. 

—The provisions concerning the tagging and 
marking are based on the fact that in Switzer¬ 
land, the civilian use of explosives is domi¬ 
nant. 

—The tagging and marking provisions required 


by the Act are reasonable and economically 
attainable for the manufacturers and im¬ 
porters of explosives. 

—Thanks to our decisions to admit not only 
one precise marking program, we provoked 
the development of new systems. And, what’s 
more, we are able to admit, at any time, tag¬ 
ging and marking systems suitable to the spe¬ 
cific type of product. 

Please, take into account that interested groups 
could freely purchase unmarked explosives until 
the end of 1982 (the total of the reported and not 
yet successfully investigated thefts of civilian ex¬ 
plosives amounts to about five U.S. tons, in real¬ 
ity it would be many times that!) We are con¬ 
vinced that these provisions serve the need of our 
police in order to be more efficient. Though we 
are aware that now, as before, it is possible to pro¬ 
cure or produce unmarked explosives, this should 
be no reason, however, not to look for new ways 
to find criminals and terrorists. The real efficiency 
of our provisions can only be revealed by the 
future. 


470 


INTERNAL STANDARD CHEMICAL LABELING OF INTACT EXPLOSIVES 
AND THE SUBSEQUENT ONLINE THIN LAYER 
FLAME IONIZATION IDENTIFICATION OF NANOGRAM QUANTITIES 
OF THESE STANDARDS IN SPENT EXPLOSIVE RESIDUES 

J. Bruce Sch/egel, President 
Schlegel Associates, Inc. 

in collaboration with 

John M. Newman, Consultant 
Newman-Howells Associates, Ltd. 


ABSTRACT. It is now possible to analyze quickly and with no laborious sample 
preparation; non-volatile, high molecular weight complex organic molecules at 
levels low enough to make chemical labeling of explosives and their subsequent de¬ 
tection feasible to incriminat would be user of explosives in a terroristic manner. 
First of all, an explosive manufacturer could ID his own product line with a 
unique, isolated, non-volatile organic chemical of choice to, without doubt, iden¬ 
tify his product. Then when utilized for a suspicious purpose, residue samples may 
be taken on-site and spotted on a Thin Layer Chromatograph with a Flame Ioniza¬ 
tion Detector. This unit is a turn key automatic system complete with a prepro¬ 
grammed data system set up for internal standard integrator chromatography anal¬ 
ysis showing a CRT and hard copy “hit ratio’’ percentage of internal standard pos¬ 
sibilities in the Basic language software executive. With this technique, the low 
minimum detectable levels required for a meaningful analysis can be attained. 
These nanogram or parts per billion levels usually attainable here-to-fore only on 
volatile compounds that can be gas chromatographed; can now be obtained on 
non-volatile compounds that will not totally disappear upon explosion. They will 
be left afterwards to allow tracing of the explosive to the buyer to seller to manu¬ 
facturer as evidence to prosecute the appropriate guilty party. Preferential Cata- 
gory: 1. Explosive Residue Analysis, 2. Explosive Analysis, 3. Remote Detection 
of Explosives. 


It is now possible to analyze quickly and with no 
laborious sample preparation; non-volatile, high 
molecular weight, complex organic molecules at 
levels low enough to make chemical labeling of ex¬ 
plosives and their subsequent detection feasible to 
incriminate would be users of explosives in a ter¬ 
roristic manner. 

First of all, an explosive manufacturer could ID 
his own product line with a unique, isolated 
non-volatile organic chemical of choice to, with¬ 
out doubt, identify his product. 

Then when utilized for a suspicious purpose, 
residue samples may be taken on-site and spotted 
on a Thin Layer Chromatograph with a Flame 
Ionization Detector. This unit is a turnkey auto¬ 


matic system complete with a preprogramed data 
system set up for internal standard integrator 
chromatography analysis showing a CRT and 
hard copy “hit ratio” percentage of internal 
standard possibilities in the Basic Language soft¬ 
ware executive. 

With this technique, the low minimum detecta¬ 
ble levels required for a meaningful analysis can 
be attained. These nanogram or parts per billion 
levels usually attainable heretofore only on vola¬ 
tile compounds than can be gas chromatographed; 
can now be obtained on non-volatile compounds 
that will not totally disappear upon explosion. 

These non-volatile compounds will be left after¬ 
wards to allow tracing of the explosive to the buy- 


471 


er to seller to manufacturer as evidence to prose¬ 
cute the appropriate guilty party. 

The TLC/FID Analyzer offers a unique method 
to the analyst by combining the universally ac¬ 
cepted technique of Thin Layer Chromatography 
with an automated quantitative detection system 
based on the classical GC/Flame Ionization prin¬ 
ciple. 

Most separations that are currently performed 
on conventinal TLC plates can be similarly made 
on the patented TLC rod (Chromarod) with 
chromatography being effected in the normal 
manner, by solvent elution. The direct and quanti¬ 
tative detection capability of an FID is applicable 
to almost all organic substances. It offers an easy, 
efficient and timesaving method for the labora¬ 
tory which has requirement to fulfill in this area of 
operation. 

Spot identification transpires without the use of 
coloring reagents or charring techniques. Peak 
areas are rapidly integrated and quantitated. Con¬ 
tinuous sample throughput permits 10 analyses to 
be made every 10 minutes. Analysis of organic 
samples which (a) are not GC volatile, (b) do not 
absorb UV or Visible Light, (c) do not flouresce or 
derivatize easily, can be analyzed. 

Screening, OC, fingerprinting, MWD and sam¬ 
ple characterization of samples can be performed 
selectively or as a precursor to further analytical 
work involving the use of other instrumenal tech¬ 
niques for confirmation. 

Built-in facilities for direct link to digital/print¬ 
out integrator; auto-zero; auxiliary switch for 
controlling and timing of external triggers are 
built-in standard to the mainframe of the instru¬ 
ment. 

The use of multi-stage solvent development 
methods offers additional separation flexibility. 
Also, a programmed pyrolysis device can auto¬ 
matically remove selected sample components 
from the Chromarod by partial FID scanning 
prior to allowing subsequent redevelopment of the 
remaining components contained within a com¬ 
plex mixture. 

The Chromarod, 0.9 mm x 152 mm (diameter), 
has a usable length of 120 mm and is coated with a 
75 um layer of specially sintered Silica Gel or Alu¬ 
mina. During the sample scaning process, the rod 
is automatically re-activated and made ready for 
repeated use (up to 100 analyses per rod can be 
made). Since the FID is insensitive to the sintered 
coating, a firm, straight baseline is achieved with 
the chromatogram revealing only the quantitative 


pattern of the separated components, plus any 
contaminant present in the sample or solvent sys¬ 
tem used. 

Three types of Chromarods are available; 
Chromarod-S, SI 1, and A. Type S and Sll are 
made from silica gel, the former material having a 
85 um particle size with the latter being made from 
5 um silica gel particles. Type A is made from alu¬ 
mina, having a 10 um particle size. Material Sll 
has a greater resolving power for certain classes of 
chemical substances. The alumina rod is normally 
used in circumstances where substances are prone 
to decomposition on silicas. It has also been found 
that the alumina material is very suitable for sam¬ 
ples which fall into the sterioisomer group. 

Chromarods can be silver nitrate or boric acid 
impregnated to enhance certain types of separa¬ 
tion. 

Sample loading on the Chromarod can range 
from 2 to 20 micrograms in a spotting solution of 
1 to 2 microliters with detection limit in the order 
of 0.067 ug/ul experienced. 

Chromarod clean-up and activation is achieved 
by blank-scanning the rods through the FID and 
by observing the stability of the meter pointer 
and/or baseline on a hard copy device. Blank 
scans may be repeated until meter permanently 
zeros signifying zero-rod contamination. 

After spotting and development, the rods re-ac- 
tivate and self-clean during the sample burn-off 
(ionization) and are ready for instant repeated use. 

Application of the sample requires care. It is 
recommended that this be undertaken with the aid 
of a microcapillary tube fitted with an efficient 
metering device with 1 ul being dispensed in five 
aliquots. Spotting is further aided by the use of the 
Spotting Guide provided. 

Development (15-40 minutes) takes place in a 
fused plate-glass chamber with the 10 rods (maxi¬ 
mum capacity per tray of rods) being retained in 
the same Rod Holder used for both sample ap¬ 
plication an scanning procedures. 

After development, the mobile phase is re¬ 
moved from the rods by placing the Rod Holder in 
an air oven for a predetermined period of time, ac¬ 
cording to the volatility of the solvent used. 

The Rod Holder frame is rapidly transferred 
from the oven to the scanning area of the Chroma¬ 
tograph to avoid atmospheric contamination of 
the rod coating. 

The start button automatically advances the 
rods in a castellated pattern through to the FID at 
a constant preselected speed variable by the opera- 


472 


tor. The components combust and are ionized to 
record quantitative individual peak values. Scans 
can be programmed to combust selected compo¬ 
nents on a rod, thus leaving those remaining to be 
further chromatographically developed and 
scanned. 


External electronic integration and print-out 
systems can be easily connected to the TLC/FID 
Chromatograph. 

Direct quantitation is assisted by adding an in¬ 
ternal standard to the sample mixture. 


EXAMPLE OF ANALYSIS BY TLC/FID CHROMATOGRAPH: 

catalyst 

Glycerine + Oleic Acid . triglycerides 

+ 

h 2 o 

(catalyst is p-toluenesulfonic acid) 

A precise volume of the result taken from the above reaction was diluted with chloroform and spotted onto a Chromarod SI 1 and 
developed. 

Conditions were: 

Stationary phase: Chromarod SI 1 
Mobile phase: Benzene; Chloroform; 

Formic Acid @ 

70:30:2 ratio, respectively 
Gas Flow: H 2 @ 160 ml/min. 

Air @ 2.0 1/min. 

Scanning Speed: 30 sec./scan 


RESULTS: Area^o 


Rod 

Number 

Tri- 

GIvceride 

Fatty 

Acid 

1,3 Di- 
Glyceride 

1,2 Di- 
Glyceride 

Mono- 

Glyceride 

1 

11.7 

48.9 

20.1 

7.0 

12.3 

2 

12.2 

47.5 

22.5 

6.9 

10.9 

3 

12.0 

49.1 

21.7 

6.0 

11.2 

4 

11.9 

48.9 

22.0 

6.3 

10.9 

5 

12.5 

47.8 

21.7 

6.7 

11.3 

6 

12.6 

48.7 

22.0 

6.3 

10.4 

7 

11.9 

49.0 

21.3 

6.8 

11.0 

8 

11.6 

48.9 

21.6 

6.4 

11.5 

9 

12.8 

48.2 

20.8 

6.9 

11.3 

10 

12.7 

46.7 

22.9 

6.8 

10.8 

X 

S.D. 

12.2 

0.43 

48.4 

0.80 

21.7 

0.80 

6.6 

0.33 

11.2 

0.51 


473 



























t. 























DETECTION OF GUNSHOT RESIDUES VIA ANALYSIS OF 
THEIR ORGANIC CONSTITUENTS 


/. Jane 

P. G. Brookes 
J. M. F. Douse 
K. A. O’Callaghan 


ABSTRACT. Procedures for the detection of organic gunshot residues on the 
hands and clothing of persons suspected of firing a weapon are described. The 
strongest evidence in this context is produced by using a scanning electron micro¬ 
scope (SEM) to detect metallic primer residues, which have characteristic shape 
and elemental composition. Unfortunately the SEM procedure is slow and this lim¬ 
its the number of cases that can be examined. Also for some primer compositions 
the SEM results are not conclusive evidence that the residue arises from a firearm 
discharge. In an attempt to find an alternative approach that could be used to rap¬ 
idly screen cases before submission for SEM analysis a study has been made of 
methods for detecting propellant residues, e.g ., nitroglycerine, diphenylamine, ni¬ 
trocellulose and inorganic nitrite. Capillary GC, TLC and HPLC with electro¬ 
chemical detection have been used and the conclusions drawn are that nitrogly¬ 
cerine and diphenylamine residues can be determined at low levels which may 
prove of value, whereas nitrocellulose and nitrite are less promising. The initial lev¬ 
els of residue deposited vary considerably with the types of weapon and ammuni¬ 
tion used. Some combinations produced so little contamination that residues could 
only be detected, using current methods, if the firer was sampled immediately, 
whereas others produced a high discharge and nitroglycerine, on hands and 
clothes, and diphenylamine, on clothes, could be detected up to 4 hours after fir¬ 
ing. Organic gunshot residue analysis has a future in forensic science but we must 
improve the sensitivity and selectivity of our techniques before it is routinely appli¬ 
cable. 


INTRODUCTION 

During the discharge of a weapon, residues 
originating from the primer, propellants, lubri¬ 
cants and bullet are deposited on the hands and 
clothes of the firer. If these gunshot residues 
(GSR) can be detected on the hands or clothes of a 
suspect then this will provide significant evidence. 
Early tests for residues relied on the detection of 
nitrite ions (Sinha and Misra 1971) but recent and 
more reliable methods are based on the detection 
of inorganic residue containing antimony, bari¬ 
um, lead and copper originating from the primer 
or the bullet. Neutron activation analysis (NAA), 
atomic absorption spectroscopy (AAS) (Kinard 
and Lundy 1975) and scanning electron micro¬ 
scopy (SEM) (Wolten et al. 1979a) are the most 
commonly used methods of inorganic residue de¬ 
tection. Of these SEM provides the most signifi¬ 


cant evidence and is the technique routinely used 
at the Metronolitan Police Forensic Science Lab¬ 
oratory. The particles detected from the primer 
residue are usually spherical and contain lead, an¬ 
timony and barium; Wolten et al. (1979b) have 
shown that these particles arise solely from the dis¬ 
charge of a firearm. However the SEM technique 
is very time consuming and is only applicable if a 
limited number of samples are routinely received. 
In addition some priming compositions, particu¬ 
larly those in .22 rimfire cartridges, contain no an¬ 
timony and the residue from these has a much 
lower evidential value. To date no one has re¬ 
ported the routine detection of organic propellant 
residues on the hands and clothes of the firer al¬ 
though detection of these would provide signifi¬ 
cant evidence of association with the discharge of 
a firearm. Additionally, since organic residue de- 


475 


tection of the primer residue would be non-de¬ 
structive, it could possibly be used as a screen, 
prior to SEM analysis to eliminate any totally 
negative samples. 

Modern smokeless powder propellants are 
based on nitrocellulose (NC), usually in a granular 
form, with additions of other organic compounds 
to improve the physical, chemical or mechanical 
properties of the powder (Mach et al. (1978a). The 
majority of powders in common use are dou¬ 
ble-based, that is they contain nitroglycerine (NG) 
as a second major constituent, but single base (NC 
as the only major constituent) powders are also 
used. Mach et al. (1978a, b) used gas chromato¬ 
graph/mass spectrometry to study the feasibility 
of detecting GSR by analysis of the organic con¬ 
stituents of the residue; they were unable to detect 
any residues using their technique. More recently, 
various workers have shown that significant quan¬ 
tities of propellant residues can be detected on the 
firer’s hand. Douse (1982) used capillary gas 
chromatography with electron capture detection 
(GC/ECD) and thin layer chromatograph (TLC) 
to detect NG and NC respectively; Bratin et al. 
(1981) used high performance liquid chromator- 
raphy (HPLC) with reductive mode electrochem¬ 
ical detection, to detect NG and 2,4-dinitroto- 
luene and oxidative mode to detect diphenylamine 
(DPA); and Lloyd (1983) used HPLC with polaro- 
graphic detection to measure NG. 

We decided, therefore, to investigate the possi¬ 
bility of using propellant residues to characterise 
GSR. Rather than attempt to measure all the com¬ 
ponents present in propellants, we concentrated 
on NC, present in every smokeless powder, and on 
NG and DPA which occur in the majority of pow¬ 
ders and for which we had sensitive analytical 
techniques. In addition we measured nitrite since 
its detection was the basis of many of the earlier 
methods of GSR analysis and we were able to 
characterise it using the same HPLC system as we 
used for DPA. 

Although the most significant evidence for hav¬ 
ing fired a weapon must come from GSR on the 
suspect’s hands, persistence of the residue is much 
greater on clothes. In the majority of cases at our 
Laboratory where GSR have been detected it has 
been on the suspects’ clothing rather than their 
hands. We therefore investigated GSR levels on 
both the hands and clothes and also in the firer’s 
hair, a further area indicated by SEM results to be 
a useful reservoir of particulate residue. 


EXPERIMENTAL 

Reagents 

NG and NC samples were pure explosives stand¬ 
ards (Propellants, Explosives and Rocket Motor 
Establishment, Waltham Abbey, Great Britain). 

DPA was a reagent grade chemical (Harrington 
Brothers Ltd., London, Great Britain). Other 
chemicals were reagent grade (May and Baker 
Ltd., Dagenham, Great Britain). 

Diethyl ether, Analar grade (BDH, Poole, 
Great Britain), was glass distilled prior to use. 
Methanol was HPLC grade (Fisons, Loughbor¬ 
ough, Great Britain). All other solvents were pesti¬ 
cide grade (Fisons). Amberlite XAD-7 (20-50 
mesh) (BDH, Dorset, Great Britain) was washed 
with distilled water, methanol, ethyl acetate, ether 
and pentane prior to use. Cotton wool (Vestric, 
London, Great Britain) was soxhlet extracted with 
ether for four hours. 

WEAPONS AND AMMUNITION 

Weapons used in our investigation were: 

Smith and Wesson Model 19-3 .357 Magnum 
revolver with 2 '/ 2 -inch barrel. 

Smith and Wesson Model 27-2 .357 Magnum 
revolver with 6-inch barrel. 

Beretta Model 71 .22LR self loading pistol. 

Sawn-off Fabrique Nabinale-Browning 12- 
bore double barrelled over and under shot¬ 
gun, barrel length 15 inches. 

Ammunition fired in these guns was: 

Winchester-Western .38 Special, 158 grain 
round nose lead. 

Smith and Wesson .357 Magnum, 158 grain 
jacketed soft point. 

Western ‘Super-X’ .357 Magnum, 158 grain 
‘Lubaby’ semiwadcutter. 

Eley ‘Club’ .22LR 

Winchester ‘Super-X’ .22LR 

Lapua .22LR 

Eley ‘Grand Prix’ 12-bore 

Laboratory loaded .38 Special containing: 

20 mg Rhodamine B (BDH) 

8.5 grains Blue Dot (Hercules, Wilming¬ 
ton, Delaware, USA) 

158 grain jacketed soft point bullet 

Laboratory loaded 12-bore cartridges con¬ 
taining: 

60 mg Rhodamine B (BDH) 

20 grains Red Dot (Hercules) 

Mark III Plaswad (Plaswad, Beeston, 
Great Britain) 

1 /t ounces lead shot. 


476 


Firing Conditions 

The firings were conducted in a 25-meter in¬ 
door range. Air extractor fans were used to clear 
the air before each test but were turned off during 
firing. Weapons were fired from the instructive 
position, that is with the gun held at waist height. 

Sampling for GSR was carried out in a section 
of the laboratory remote from the range in order 
to avoid contamination, and this necessitated a 
minimum delay of five minutes between firing and 
sampling. 

During the experiments with dye loaded car¬ 
tridges the firer wore a disposable ‘waxed’ paper 
overall and paper toweling around the head. After 
firing, the dye was visualised by spraying the areas 
of interest with deionised water and viewing them 
under a long wave ultra-violet lamp. 

N.B. During a number of these tests using the 
dye loaded cartridges, bullets were retained in the 
barrel. This is a hazardous phenomenon and was 
almost certainly the result of using a reduced pro¬ 
pellant charge in these cartridges. 

Analysis of NG and NC 

The analysis of NG by GC/ECD and TLC, and 
of NC by TLC, was performed using the method 
described by Douse (1982). 

GC/ECD: 

The gas chromatograph (Varian Model 1800) 
was used with a home-made glass lined injection 
port and a Carlo Erba Model HT-25 Electron 
Capture Detector operated in the constant current 
mode at a potential of 50V and a pulse width of 1 
iu sec. Conditions: column 21 m x 0.25 mm (i.d.) 
flexible-fused silica capillary externally coated 
with polyimide (Phase Separations Ltd., Queens- 
ferry, Great Britain); stationary phase, OV 101; 
injection port temperature, 165 °C; detector tem¬ 
perature 250 °C; temperature program, 25 °C held 
for 30 sec then programmed at 40°C/min to 
200°C, cool down time 4 min; carrier gas, helium 
at 30 ml/min (25 °C); make-up gas 5% 
methane-argon at 13 ml/min; injection solvent, 
ether or ethyl acetate, usually 0.5 pi. 

TLC: 

TLC plates were DC-Alufolien Kieselgel 60F 
254 (5 cm x 7.5 cm x 0.2 mm) (Merck, Darmstadt, 
G.F.R.). The eluting solvent for NG was 
toluene/cyclohexane (7/3 by volume) and for NC 
acetone/methanol (3/2 by volume). 

Location was by Griess reagent spray. The 
plates were eluted and the solvent evaporated us¬ 
ing a stream of warm air. They were then sprayed 


with IN sodium hydroxide solution and heated to 
150°C for 5 min. The plates were then sprayed 
with a solution of sulphanilamide (8 g) and 
N-l-naphthylethylenediamine dihydrochloride 
(0.4 g) (Sigma, Poole, Great Britain) in 8% ortho- 
phosphoric acid (100 ml). NC and NG both devel¬ 
oped a red colouration. 

ANALYSIS OF DPA AND NITRITE 

DPA and nitrite were analysed by HPLC with 
oxidative mode electrochemical detection, using a 
strong anion-exchange column where both were 
to be detected and reverse phase column for DPA 
alone. 

The conditions for DPA and nitrite analysis 
were: 

Pump, single piston reciprocating pump (Model 
400, Applied Chromatography Systems Ltd., 
Luton, Great Britain); column, 12.5 cm x 4.9 mm 
(i.d.) stainless steel tube slurry packed with a sili¬ 
ca-based strong anion exchanger prepared by the 
method of Wheals (1983); injector, valve injector 
fitted with a 20 p 1 loop (Negretti and Zambra, 
Southampton, Great Britain); eluent, 1.75 g of cit¬ 
ric acid dissolved in 2.5 1 of methanol/water 
(55/45 by volume), the solution being adjusted to 
pH 5.5 with ammonium hydroxide solution; flow, 

1 ml/min; injection, samples dissolved in eluent. 

The eluent was monitored with an oxidative 
mode electrochemical detector at 0.8 V applied 
potential versus a silver/silver chloride reference 
electrode. The detector cell was laboratory con¬ 
structed (White 1979) with a glassy carbon work¬ 
ing electrode; the electronics unit was a commer¬ 
cial potentiostat (Model 174A, EG & G Princeton 
Applied Research Ltd., Bracknell, Berks., Great 
Britain). 

For DPA alone the conditions were identical ex¬ 
cept that the column packing was Spherisorb 
(Phase Separations Ltd.) and the eluent meth- 
anol/H 2 0 ratio was 65/35. 

Sampling from Hands 

Hand swabs were obtained by repeatedly scrub¬ 
bing the back of the firing hand using a cotton 
wool swab (approx. 40 mg) moistened with ether. 
The swab was extracted by successive washing 
with small portions of ether (total volume 12 ml) 
in a beaker using a glass rod. The combined ex¬ 
tracts were centrifuged to remove traces of skin 
debris, and the clear supernatant decanted into a 
silanized conical tube. The ether was evaporated 
down to near dryness using a stream of nitrogen 
and the last traces allowed to evaporate at room 


477 


temperature. Pentane (3 ml) was added to the resi¬ 
due and the resulting solution transferred to a 
screw capped vial containing Amberlite XAD-7 
beads (10 mg dry weight). The resulting mixture 
was shaken for 15 minutes so that the beads circu¬ 
lated throughout the solution. The pentane was 
then decanted using a pasteur pipette and the 
beads thoroughly rinsed using clean pentane. 

The residual traces of pentane were removed 
with a stream of nitrogen and the dry beads trans¬ 
ferred to a clean vial. The beads were then ex¬ 
tracted with 50 ^1 of ethyl acetate and 1 ptl of this 
extract was analysed for NG by GC/ECD. 

For the detection of NC, the insoluble residue 
from the swab was extracted with acetone. The 
acetone was then concentrated to low volume and 
analysed by TLC. 

Sampling from Clothes 

Residues from clothes were collected by vacu¬ 
uming using the barrel of a 2 ml glass Luer-Lock 
syringe. (Chance Brothers, Malvern Link, Wor¬ 
cestershire, Great Britain) which was attached to 
the laboratory vacuum line by the syringe 
Luer-fitting. A glass-fibre disc (Type AP-Prefit- 
ter, Millipore Corporation, Bedford, Massachu¬ 
setts, USA), cut to slightly greater size than the 
syringe barrel and pushed firmly on to the base of 
the syringe, served to retain the particulate matter. 

When each sampling was finished the syringe 
was detached from the vacuum line and the Luer 
end was sealed with a PTFE plug. Redistilled ether 
(2 ml) was added and the syringe allowed to stand 
for 10 minutes to extract the residue. The PTFE 
plug was removed, the ether was drained into a 10 
ml glass evaporation tube and concentrated to ap¬ 
proximately 100 ^1 under a stream of nitrogen. 

An aliquot of this concentrate was then injected 
into the GC/ECD for analysis of NG. The remain¬ 
der was allowed to evaporate to dryness and the 
resulting residue taken up in 100 /ul of HPLC elu¬ 
ent for the analysis of DPA. 

If an analysis for NC was to be carried out, the 
glass fibre filter paper was removed and extracted 
in an ultrasonic bath for 10 minutes in acetone. 
The acetone was then removed, evaporated to vir¬ 
tual dryness and applied to the TLC plate. 

Results and Discussion 

Preliminary trials with both revolvers and shot¬ 
guns using cartridges loaded with a mixture of 
propellant and dye indicated that the main areas 
where the propellant residues were deposited were 


the firing hand, the arms and the front of the 
chest. 

The quantity and position of the dye deposited 
varied with weapons used. For instance the quan¬ 
tity deposited on the firer by single- and dou¬ 
ble-barreled shotguns was less than with revolv¬ 
ers, unless the shotguns were opened directly after 
firing allowing residues to escape from the other¬ 
wise sealed breech. 

Dye was found on the head of the firer but in 
smaller quantities than in other areas. Indeed, in 
later trials with normal ammunition, we were un¬ 
able to detect any propellant residue on the firer’s 
hair even though this is a site where inorganic resi¬ 
dues have regulaly been detected in routine case¬ 
work using the SEM/EDX technique. 

As a result of these initial trials two main areas 
were chosen for examination, the back of the fir¬ 
ing hand and the clothing on the arms and the 
front of the chest. 

Nitrite Analysis 

The use of a strong anion exchange column 
packing which additionally exhibited a degree of 
reverse phase retention (Wheals 1983) permitted 



Figure 1. Analysis of DPA and nitrite by HPLC on a strong 
anion exchange column with oxidative mode electrochemical 
detection at + 0.8 V applied potential. A-20 pi of a solution of 
nitrite (1) and DPA (2) each at 0.5 pg/ml in eluent. B-20pl of a 
100 pg/ml solution of Winchester and Western .357 magnum 
propellant, sample originally dissolved at 1 mg/ml in ethyl ace¬ 
tate and diluted to lOOpg/ml with eluent. Experimental condi¬ 
tions as described in text. 


478 




















the characterisation of both nitrite and DPA in a 
single chromatographic analysis. Both compounds 
are readily oxidized and can be detected with ex¬ 
cellent sensitivity by an oxidative mode electro¬ 
chemical detector (Figure 1). 

Nitrite is however an environmental contamin¬ 
ant and initial tests showed that levels of nitrite 
found on either the hands or clothes of subjects 
who had fired a gun were not significantly higher 
than those found before firing. This confirms pre¬ 
vious experiences where attempts had been made 
to use the presence of nitrite on the hand of a sus¬ 
pect as evidence of use of a firearm (Sinha and 
Misra 1971). The work on the analysis of nitrite 
was not pursued in the context of such evidence, 
but the method could still be potentially useful in 
monitoring the stability of NC in propellants by 
virtue of the nitrite produced by its decomposi¬ 
tion. 

To eliminate interference from nitrite, the sys¬ 
tem which was subsequently used for the analysis 
of DPA was a conventional reverse phase column 
on which the nitrite was not retained. 

Hand Samples 

Unless a high level of GSR was present on the 
subject’s hands (levels corresponding to those on 
samples taken immediately after firing) NC and 
DPA were not detectable using present methods; 
NC because of the relative insensitivity of the TLC 
technique and DPA because of interference from 
contaminants in the hand swab extracts. Hand 
swab samples were, therefore, normally only ana¬ 
lysed for NG. The levels of NG found on the back 
of the firing hand, sampled almost immediately 
after firing, varied from 2 y .g to below the detec¬ 
tion limit of the method depending on the weapon 
and ammunition used. 

In an attempt to determine the nature of the 
residue deposited on the hand, some experiments 
were carried out in which samples were taken by 
vacuuming the back of the firing hand prior to the 
normal swabbing procedure. Similar amounts of 
NG were found in the hand swab and in vacuum 
samples from hands immediately after firing. NG 
was not detected in the vacuum samples from 
hands taken Vi hour or longer after firing, despite 
considerable quantities still being detected on 
hand swabs. These results indicate that NG is de¬ 
posited on the hand as both fume and particulate 
matter, the latter falling rapidly from the hand 
with normal activity. Figure 2 shows chromato¬ 
grams of NG recovered from the hands of subjects 
up to two hours after they had fired a revolver. 


Clothes Samples 

The vacuum sampling technique is simple and 
rapid and provides relatively uncontaminated 
samples of GSR for analysis. NG, DPA and NC 
can all be detected at low levels without a sample 
clean-up. The sampling certainly appears to be ef¬ 
ficient since no further residue has been detected 
on a second sampling. However, the nature of the 
technique is such that only particulate GSR or par¬ 
ticulate matter coated with NG can be detected. 

The initial levels of NG found on clothes sam¬ 
ples varied from 11 \xg to a level below the detec¬ 
tion limit of the method, depending on the weap¬ 
on and ammunition used. Almost invariably high¬ 
er quantities of GSR were detected on clothes than 
on hands and the persistence was much greater. 

Figures 3 and 4 show NG and DPA levels found 
on clothes samples six hours after a weapon had 
been fired. NC on clothes was also detectable by 
TLC for several hours after the firing had taken 
place. 

The ratio of NG to DPA in samples taken from 
clothing after 20 firing experiments using the 
Smith and Wesson model 19 revolver ranged from 
10 to 65 with an average value of 27. The average 
NG/DPA ratio in the original propellent extracted 
from three unfired cartridges was 49 (44-55). 

It is not apparent from the results so far wheth¬ 
er the variation in the ratio is due to processes at 
work during firing or some feature of the sam¬ 
pling technique. 

Factors Affecting the Level of GSR Found 

The factors which affect the level of organic 
GSR found on a firer are numerous and would 
seem to be similar to those reported for primer 
residues (Cornelis and Timperman 1974). In ex¬ 
periments to show the effect of one particular fac¬ 
tor it is necessary to perform many replicate fir¬ 
ings while rigorously controlling all the other vari¬ 
ables. 

In this initial investigation it has not been possi¬ 
ble to do more than verify that the most important 
factors have the effects that both logic and the re¬ 
sults of previous trials would suggest. The factors 
which, from our experiments, had a considerable 
effect on GSR levels were: the type of weapon; 
ammunition; nature of the skin and clothes, and 
the time and activity since firing. 

Type of Weapon 

Weapons which produce discharge from the 
breech would be expected to give rise to higher lev¬ 
els of detectable GSR on the firer than those in 


479 



1 1 0 2 1 0 2 1 0 mir 

j _ ■ _i -1-*- 1 -1-1_1 

Figure 2. Nitroglycerine from hands using GC/ECD. Three subjects each fired three rounds of Winchester .38 Special ammunition 
from a Smith and Wesson Model 19 revolver. A-sampled after Vz hour (corresponds to 140 ng of NG (1) on the hand), B-sampled 
after 1 hour (78 ng NG), C-samples after 2 hours (10 ng NG). Conditions as in text. 





Figure 3. Nitroglycerine (1) from clothes using GC/ECD. A-Blank wool sweater extract, / 40 of sample injected (* NG retention dis¬ 
tance). B-Wool sweater extract 6 hours after firing 5 rounds of Winchester and Western Magnum .357 ammunition from a Model 
19 revolver, !/ 0 oo of sample injected. C-100 pg of NG injected. Peaks other than NG in B & C arise from a dirty injection port. 


480 






















































































which all the residue is discharged from the muz¬ 
zle, and this was indeed found to be the case. Re¬ 
volvers produced high initial levels of GSR, up to 
11 ^g NG on clothes and 2 jig on hands, whereas 
sealed breech shotguns and rifles gave very low or 
even undetectable amounts unless the breech was 
opened soon after firing the weapon. The cleanli¬ 
ness of the weapon prior to firing will almost cer¬ 
tainly affect the nature and amount of residue de¬ 
posited on the firer; however, we have not as yet 
investigated this area. The correlation between the 
composition of the propellant and the composi¬ 
tion of the resulting organic residue is another 
area which remains to be investigated. 

The number of rounds fired did not seem to 
have a marked effect on the quantity of residues 
detected; this result agrees with that reported for 
primer residues by Cornelis and Timperman 
(1974) but it is perhaps an unexpected one and 
merits a more rigorous investigation. 

Nature of Skin or Clothes 

Samples taken from clothes made of materials 
which trap particulate matter show higher initial 


levels and greater persistence of organic GSR than 
clothes made from ‘smooth’ materials. The initial 
levels of GSR detected on hands varied consider¬ 
ably both between subjects and on the same sub¬ 
ject on different days. This was true even when all 
other controllable variables were kept constant. 
This variation would seem to be due to variation 
in the skin condition and other related factors. 

Time and Activity Between Firing and Sampling 

In the experiments to determine the persistence 
of organic GSR the firers were asked to behave 
normally between firing and sampling but not to 
wash their hands. With hand samples, a rapid ini¬ 
tial loss of GSR was observed followed by a slight¬ 
ly less rapid loss of the remaining residue. From 
our results we would expect to be able to detect 
NG on the hand of a firer some two hours after 
firing a revolver. 

The persistence of GSR on clothes is much 
greater. In tests where firings were carried out 
with a revolver, we were able to detect NG, DPA 
and NC six hours after the firings had taken place 
with the subjects wearing a variety of clothes. 



Figure 4. Diphenylamine (1) from clothes by HPLC using a reverse phase column, 65/35 methanol/water eluent and electrochem¬ 
ical detection at + 0.8 V. A-extract from a blank wool sweater (Vi sample injected). B-wool sweater 6 hours after firing 5 rounds of 
Winchester and Western Magnum .357 ammunition from the Model 19 revolver. C-5 ng/ml DPA standard in eluent (= 100 pg in¬ 
jected). Other conditions as in text. 


481 































Trials in which the subjects fired one day and were 
sampled the next produced no GSR, whe r eas GSR 
was readily detectable the next day on a jumper 
which had been removed immediately after firing 
and stored undisturbed. These results imply that 
the residue is lost by physical disturbance rather 
than by any chemical degradation. To confirm 
this cotton sheets were seeded with GSR by hold¬ 
ing them one meter from the side of the revolver 
while five rounds were fired. The sheets were then 
stored undisturbed and were sampled periodically 
to check the level of GSR remaining; significant 
quantities of GSR were still detectable two months 
after the firing experiment. 

CONCLUSIONS 

The work reported here was carried out in order 
to investigate the possibility of using the presence 
of organic GSR to provide evidence of a suspect’s 
connection with the discharge of a firearm. The 
detection of organic GSR is potentially more use¬ 
ful than inorganic residue analysis by AAS or 
NAA. The analysis can be equally rapid and no 
problem should be encountered with environmen¬ 
tal levels. 

The work is at a very early stage and much more 
needs to be done in order to determine the nature, 
origin and persistence of the residues. However, 
the results so far show that the detection of organ¬ 
ic GSR is a very promising area for further investi¬ 
gation. NG can be detected on hands two hours 
after firing a revolver but the sensitivity and hence 
the usefulness of the technique is limited by the 
lack of selectivity of the GC/ECD method. NG, 
DPA and NC can all be detected on clothes for a 
significant period after firing and it is likely that 
we will be applying this determination in the near 
future to casework samples as a screen prior to 
SEM analysis. 

Before this is a possibility a number of advances 
in the technique of organic analysis must be made. 
We need a more selective method for NG detec¬ 
tion. GC-MS using negative ion chemical ionisa¬ 
tion or GC coupled to a Thermal Energy Analyser 
are the logical possibilities. 

We also need an improved method of NC anal¬ 
ysis. Size exclusion chromatography with reduc¬ 
tive mode electrochemical detection should pro¬ 
vide this. 

These improvements are applications of existing 
proven methods, rather than fundamental new de¬ 
velopments, and it is easy to predict therefore that 


organic GSR analysis will find increasing use in 
the near future. 


REFERENCES 

Bra tin, K., Kissinger, P. T., Briner, R. C., 
Brunt/ett, C. S., (1981). Determination of nitro 
aromatic, nitramine and nitrate ester explosive 
compounds in explosive mixtures and gunshot 
residue by Liquid Chromatography and reduc¬ 
tive elctrochemical detection. Anal. Chim. 
Acta. 1981 130(2)295. 

Cornells, R., and Timperman, J., (1974). Gunfir¬ 
ing detection method based on Sb, Ba, Pa and 
Hg deposits on hands. Evaluation of the cred¬ 
ibility of the test. Medicine Sci. Law, April pp 
31-49. 

Douse, J. M. F., (1982). Trace analysis of explo¬ 
sives in handswab extracts using Amberlite 
XAD-7 porous polymer beads, silica capillary 
column Gas Chromatography with Electron 
Capture Detection and Thin Layer Chromato¬ 
graphy. J. Chromatogr. 234 pp 415-425. 

Kinard, W. D., and Lundy, D. R. (1975). A com¬ 
parison of Neutron Activation Analysis and 
Atomic Absorption Spectroscopy on Gunshot 
Residue. ACS Symposium Series 13, American 
Chemical Society, Washington, D.C. pp 
97-107. 

Lloyd, J. B. F., (1983). Clean-up procedures for 
the examination of swabs for explosives traces 
by High Performance Liquid Chromatography 
with Electrochemical Detection at a pendant 
mercury drop electrode. J. Chromatogr. 261 pp 
391-406. 

Mach, M. H., Pal/os, A., and Jones, P. F. (1978). 
Feasibility of gunshot residue detection via its 
organic constituents. Part I: Analysis of 
smokeless powders by combined Gas Chrom¬ 
atography-Chemical Ionisation Mass Spectro¬ 
metry. J. For. Sci. 23, No 3, pp 433-445. 

Mach, M. H., Pal/os, A., and Jones, P. F. (1978). 
Feasibility of gunshot residue detection via its 
organic constituents. Part II; A Gas Chroma¬ 
tography-Mass Spectrometry method. J. For. 
Sci. 23, No 3, pp 446-455. 

Sinha, J. K. and Misra, G. J., (1971). Detection 
of powder particles at the crime scene. J. For. 
Sci., 16, 109-111. 

Wheals, B. B. (1983). A multiple column and de¬ 
tector approach to anion screening by isocratic 
high performance liquid chromatography. J. 
Chromatogr. 262 61-76. 


482 


White, M. W. (1979). Determination of morphine 
and its major metabolite, morphine-3- 
glucuronide, in blood by high performance liq¬ 
uid chromatography with electrochemical detec¬ 
tion. J. Chromatogr. 178, pp 229-240. 

Wolten, G. M., Nesbitt, R. S., Calloway, A. .R., 
Loper, G. L., and Jones, P. F. (1979a). Particle 
analysis for the detection of gunshot residue. 


I: Scanning Electron Microscopy/Energy Dis¬ 
persive X-ray characterisation of hand deposits 
from firing. J. For. Sci., 24, No 2 pp 409-422. 

Wolten, G. M., Nesbitt, R. S., Calloway, A. R., 
Loper, G. L., (1979b). Particle analysis for the 
detection of gunshot residue. II: Occupational 
and environmental particles. J. For. Sci., 24 No 
2, pp 423-430. 


483 
































NEW MEASUREMENT STUDIES ON THE EFFECTS OF THE IEDS 


Werner Wildner + 

Bundeskriminalamt 
D 6200 Wiesbaden 
Federal Republic of Germany 


ABSTRACT. As in other countries, attacks by improvised explosive devices 
(IEDs) in the scene of politically motivated crime play an important role in FRG, 
too. The right assessment of their effects is of great importance both in order to 
ward off danger and from a forensic point of view. Indeed, everywhere attempts 
are made to answer this question by comparative blastings but mostly the appro¬ 
priate methods are not available to obtain really evident and comparable measur¬ 
ing results. Therefore, at Bundeskriminalamt (BKA) methods of investigation have 
been established which can furnish (in a scientific sense) objective measurement 
data on the effects of IEDs. Measurement methods and apparatus for the experi¬ 
mental detection of the blast and fragmentation effects of IEDs are described since 
they are the most hazardous for human beings. The problems of providing condi¬ 
tions for carrying out suitable studies on explosion effects by means of compara¬ 
tive blastings are discussed. Exemplary measurement results and their conclusions 
are presented. 


INTRODUCTION 

First, the following should be premised: If 
there is discussion about new measurement stud¬ 
ies, it only means that the application of such 
studies, as they are reported here, is new to the 
field of criminal investigation, and new to IEDs 
(improvised explosive devices) as objects. The 
methods themselves are not new at all, since they 
have been applied for a very long time to the field 
of testing new weapons for military use. This fact, 
on the other hand, implies that only IEDs should 
be studied by those means; for, the complete data 
of the effects and performance of commercial and 
military explosives and of all kinds of weapons are 
already available. In those cases, the correspond¬ 
ing tables should be used and calculations should 
be made before carrying out large-scale experi¬ 
ments. 

The aim in the case of measurement studies on 
the effects of IEDs is to get data that fulfull the 
following conditions: 

—They must be comparable with the usual 
classification data of military weapons 
(bombs, war heads etc.). 

—They must be obtained in a clearly defined 

+ Dr. rer. nat.. Physicist, Forensic Science Laborabory 


manner, concerning both the objects and the 
measurement methods. This means any team 
of technicians must be in a position to repro¬ 
duce the results. 

We want to achieve some method of character¬ 
ising the effects of IEDs by numerical values 
which would render unnecessary any dependence 
on unsuitable descriptions in words. If we are suc¬ 
cessful with our project the courts will be provided 
with a better basis for judging offences committed 
in connection with IEDs. And, on the other hand, 
the police, in particular bomb technicians, will dis¬ 
pose of better facilities for estimating the hazards 
of IEDs. We have restricted our studies to the 
explosion effects on human beings, and we have 
only considered the effects of blast pressure and 
fragmentation, since they are the most important 
ones. 

PHYSICAL BASIS 

Below, a brief review of the physical processes is 
given that occur when an IED explodes. We are 
not dealing here with detonating high explosives— 
for their behavior and effects are well known—but 
we must examine the improvised, “home-made” 
mixtures, which cannot normally detonate. Their 
reaction is just deflagration, and therefore bombs 


485 



Table 1. PHYSIOLOGICAL EFFECTS OF BLAST OVERPRESSURE ON HUMAN BEINGS 


effects 

overpressure (norm, refl.) 

short duration 

«3 ms) 

long duration 

(>3 ms) 


bar 

psi 

bar 

psi 

eardrum failure 





threshold (1 percent) 

0.35 

5 

0.2 

3 

50 percent 

1.0 

14.5 

0.45 

6.5 

90 percent 

— 

— 

0.85 

12 

lung damage 





threshold (1 percent) 

2.5 

36 

1.0 

14.5 

50 percent 

3.5 

51 

1.5 

22 

90 percent 

5.5 

80 

2.0 

29 


charged with these mixtures require a strong me¬ 
tallic container wall. After ignition—there is no 
need of a detonator—the increasing internal gas 
pressure destroys the container, and by the sudden 
pressure jump at this moment an air blast wave is 
created. This shock wave propagates faster than 
the fumes and causes a long-range effect of the 
explosion. By contrast, the pressure of the fumes, 
i.e., the overpressure of the gases originating from 
the solid (or liquid) explosive, constitutes a short- 
range effect. The waveform of the air-blast pres¬ 
sure looks as shown in Figure 1. This is the time- 
varying pressure, which is observed in a fixed 
place at a certain distance from the explosion 
center. The pressure jumps straight to its maxi¬ 
mum value when the wave front arrives, but de¬ 
creases more slowly and passes through a slight 
but long-lasting vacuum range before equalizing 
to normal atmospheric pressure. The decisive 
quantities for the physiological effects of the blast 
wave are the maximum pressure as well as the 
duration of the positive pulse. This is indicated in 
Table 1 where a distinction is made between in¬ 
juries caused by exposure to short and to long 
pressure duration. The limit between “short” and 
“long” should be assumed to be a value of about 
3 milliseconds. 

It may be taken from these empiric results, 
which have their origin in the relevant literature 
(Cohen, 1968, Diephold et al. 1970, Jensen 1972), 
that exposure to long-lasting pressure causes more 
serious injuries at the same maximum value than 
exposure to pulse-like pressure. This implies that 
care must be taken in measurements to record 
both quantities, the maximum overpressure and 
the pulse length. 

As mentioned before, the fragmentation effects 


are at least as important as the blast wave effects. 
Since home-made explosives normally need the 
metallic confinement, fragments must be ex¬ 
pected. The probability of their causing injuries 
can be correlated with their kinetic energy. It is a 
good approximation, if we assume that the 
threshold value for lethal injuries is about 80 
Joules (which corresponds to 60 ft.-lb.). There¬ 
fore, in military language, fragments with a higher 
energy than this value are called “effective frag¬ 
ments” (French and Callender, 1962, Heiser, 
1974). The measurement method of this threshold, 
as pointed out below, represents a simplified 
possibility for the detection of the fragmentation 
effects. 



t ime 

Figure 1. Schematic waveform of air blast pressure. 

EXPERIMENTAL 

Below, the experimental setup for the detection 
of the blast wave and the fragment energy is de¬ 
scribed. 

First, the blast wave measurement! As men- 


486 





















tioned before, it is important to get the informa¬ 
tion on the maximum pressure as well as on the 
pulse duration. This means that the entire time- 
varying pressure curve must be detected. The suit¬ 
able probes for this task are piezoelectric pressure 
transducers. Modern quartz transducers with 
built-in amplifiers as shown in Figure 2, offer a lot 
of advantages: 

—high linearity over a wide range, 

—high resonance frequency and 
—high level voltage output at low output impe¬ 
dance, which allows the use in moist or dirty 
field environments. 





Figure 2. Piezoelectric pressure transducer with built-in 
amplifier. 

Their electric signals can be registered in a dig¬ 
ital storing transient recorder and read out to a 
long-time store, for example a magnetic tape or a 
floppy disk. This enables all the further possibili¬ 
ties of computer analysis of measurement data. 
The schematic setup for a pressure detection 
experiment is shown in Figure 3. Several pressure 
probes containing the quartz transducers are posi¬ 
tioned around the explosion center in different 
directions and distances, in order to furnish 
information on the local variation of the pressure. 
The electric signals are registered in the parallel 
channels of a transient recorder. For preliminary 
field analysis, a display unit is connected to make 
the curves visible. For the final computer analysis, 
the data are stored in a magnetic tape recorder. 

The main problem in using quartz transducers 
consists in mounting these correctly in a pressure 
probe. Care must be taken that the transducer is 
mounted in such a way that the pressure detected 
is clearly defined physically. The pressure in a free 



Figure 3. Total setup for blast pressure detection. 

shock wave can be detected as shown in Figure 4. 
The transducer is perpendicular to the movement 
direction of the wave front and receives informa¬ 
tion on the “static pressure”. The special shape of 
the probe with the peak pointed towards the 
explosion center prevents perturbation of the wave 
front, and thus wrong measurement. Besides, this 
setup represents effective protection from damage 
by fragment impacts. For the correct detection of 
the reflected pressure, the transducer must be inte- 


shock front 



Figure 4. Pressure probe for the detection of static pressure in 
a free shock wave (schematically). 


487 
























































/ 

/ 

^ ^ ' 

\ / / incident 

N / shock front 

reflected \ 

shock front \ 

' / 



Figure 5. Pressure probe for the detection of reflected pressure 
(schematically). 

grated in a plane metal plate, as shown schemat¬ 
ically in Figure 5. 

As mentioned before, there is a simplified 
method of detecting the fragment energy without 
using an expensive and sophisticated method such 
as X-ray flash photography. Since the kinetic 
energy of a fragment corresponds to its capability 
of penetrating a certain material of a certain thick¬ 
ness, and threshold energy may easily be measured 
by using one specific target material. Due to the 
quoted definition of “effective fragments”, the 



Figure 6. Schematic setup of a simplified “fragmentation 
garden”. 

important threshold of 80 Joules may be found 
out with the help of steel plates of a thickness of 
1.5 mm. The experimental setup is called a “frag¬ 
mentation garden”. The plates are positioned in a 
certain manner around the IED, so that informa¬ 
tion may be obtained on the fragmentation haz¬ 
ards in different directions and at varying dis¬ 
tances. We have used several simplified setups, for 
example, the one shown schematically in Figure 6. 
Figure 7 and Figure 8 show this fragmentation 



Figure 7. Fragmentation garden before a test explosion. 


488 












Figure 8. Fragmentation garden after a test explosion. 


garden in practical use before and after a test 
explosion. The advantage of this fragmentation 
garden method is that it furnishes the distribution 
of lethal fragments in dependence on direction 
and distance, and besides leaves a very clear pic¬ 
ture. 

To complete the fragmentation analysis we need 
to establish the so called “fragmentation pat¬ 
tern”. For this purpose, all fragments must be re¬ 
covered by means of an IED explosion under sand 



or under water (Figure 9). It is important to 
provide for an air environment of the bomb, so 
that natural fragmentation is rendered possible 
without direct confinement by sand or water. 
Figure 10 shows a typical fragmentation pattern of 
a pipe bomb that was filled with a home-made im¬ 
provised explosive. The total number of fragments 
is smaller than in the case of a highly explosive 
charge. The mass distribution of the fragments is 
usually summarized in a diagram (Figure 11), 
where the number of fragments is plotted against 
their mass. 

Discussion About the Application of These 
Methods 

The methods described just now may be applied 
to two investigation fields: To actual cases or to 
systematic research on IED effects. The prior 
condition for carrying out such studies in actual 
cases is the complete knowledge of the IED con¬ 
struction. The exact details of the container (its 
material, size, thickness), of the charge (its com¬ 
position, particle sizes, quality of mixture) and of 
the ignition must be known. Otherwise, any 
experimental results by comparative blastings with 


489 












































number of fragments 






Figure 10. Fragmentation pattern of an IED (double walled pipe bomb). 


reconstructed bombs are irrelevant and worthless. 
This must be considered especially in those cases 
where only information on the explosive residues 
is available. On the other hand, the great expenses 
of these studies mean a restriction of their applica- 



mass of fragments [ g 1 

Figure 11. Fragment mass distribution diagram (correspond¬ 
ing to the fragmentation pattern of fig. 10). 


tion on just the very important cases. 

More significant results should be expected 
from systematic studies on the effects of lEDs. It 
is our aim to get the relevant information on the 
most frequent types of IEDs. For that purpose, we 
have started a series of investigations which, how¬ 
ever, is restricted to a few idealized bomb types. 
The mixture ratio of the charges has been varied 
and different types of ignition have been used. 
Each experiment has to be repeated several times 
in order to provide for statistic safety. While 
carrying out this long-term program which may 
take several years, we are going to publish the 
individual results for use in the police field. 

EXEMPLARY RESULTS 

Below, some examples of experimental results 
and their conclusions are presented. First let us 
consider the application to actual cases! In the 
first example, a pipe bomb filled with a pyrotech- 
nical flash mixture and a small quantity of an 
added propellant was investigated. Several speci¬ 
mens of the IED, secured in a terrorist appart- 
ment, were reconstructed (Figure 12). The wave- 


490 


















Table 2. DISTRIBUTION OF EFFECTIVE FRAGMENTS IN EXAMPLE 1. 


distance 


2m 

2m 

2m 

3m 

3m 

5m 

direction 


90° 

45° 

0° 

45° 

90° 

0° 

effective 

1. 

3 

0 

4 

0 

2 

4 

fragments 

2. 

2 

0 

5 

0 

4 

4 


form of the pressure curve, detected at a distance 
of 4 m from the explosion center is shown in 
Figure 13. The duration of the pressure pulse is 
shorter than 3 ms, which means that it shows the 
same time behavior as the blast wave of a high 
explosive of the corresponding charge weight. The 
maximum value of about 0.5 bar indicates that at 
this distance range the probability of eardrum fail¬ 
ure is about 10 percent. Since this was our first in¬ 
vestigation and we had not yet got the complete 
equipment, we did not study the pressure at 
various shorter distances. An estimative calcula¬ 
tion furnished the pressure threshold of 2.5 bar 
for (fatal) lung damage at about 1.5 m distance. 
The results of fragmentation garden experiments 
are shown in Table 2. Effective (lethal) fragments 
were detected at all distance ranges investigated, 


but there was a significant direction dependence of 
fragment distribution with maxima in, and per¬ 
pendicular to, the axis of the pipe and minima in 
all 45 degree directions. A fragmentation pattern 
and a fragment mass distribution diagram of this 
IED are shown in Figure 10 and 11. 

In the next example an IED consisting of a mili¬ 
tary handgrenade (type MK 2) with an improvised 
charge of 30 g of a propellant was to be investi¬ 
gated. There were only weak pressure effects 
(about 0.5 bar at 1 m distance and <0.1 bar at 2 m 
distance) but effective fragments could be detected 
up to a distance of 4 m. The fragmentation pat¬ 
tern (Figure 14) shows, that not all the predeter¬ 
mined breaking points were ruptured. Of course, 
this IED is not as hazardous as a military handgre¬ 
nade with a highly explosive charge, but neverthe- 



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CM 


in co 

CM CM 


CM 


GO O’) 
CM CM 


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po co a po po to po 


oo cn 
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Figure 12. Construction of the IED in example 1. 


CM 


491 












overpressure Cbarll 



l i me C ms 3 

Figure 13. Overpressure waveform of the IED in example 1. 


less it cannot be called harmless, either. 

The object of the third example was a home¬ 
made firecracker which was composed of a lot of 
charges of smaller commercial pyrotechnical ar¬ 
ticles. As a confinement there was only aluminum 
foil and adhesive tape so that no fragmentation 
was to be expected. However, the pressure effects 
were considerable. Figure 15 shows the curve de¬ 
tected at a distance of 3m, which again represents 
the same time behavior as the blast wave of a high 
explosive of the corresponding charge weight. The 
maximum values of the static pressure in the free 
shock front (without reflection) were about o.6 



III! 

lilllllllllllllllll 

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llllllll! 

111111111 

llllllll! 

llllllll! 

lllllllll 

lllllllll 

lllllllll 

lilllllllllllllllll 

lllllllll 

lllllllll 

lllllllll 

lllllllll 

lllllllll 

lllllllll 

llllllll! 

lllllllll 

2 

55! 7Z 

CNI 

CO 

SC 

K? 

58 


55 

<3 

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52 

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Figure 14. Fragmentation pattern of the IED in example 2. 


492 

























n 

L 

0 



bar at a distance of 1 m and > 2.5 bar at a distance 
of 0.5 m. This implies that the possibility of lung 
damage with fatal consequences in the short-range 
area cannot be excluded. 

Finally, some preliminary results of the first 
series of systematic research on IED effects will be 
presented. As a first kind of idealized bomb con¬ 
tainer we have chosen 2-inch seamless water pipes 
of 25 cm length with two screw caps. The first 
mixture we have been studying is a very common 
home-made explosive in the German crime scene. 
It consists of a herbicide, containing sodium 
chlorate with 25 percent sodium chloride, and of 
sugar. The ratio we have been using first is 3.5 
parts of the herbicide with 1 part of sugar, which 
represents nearly the ideal stoichiometric composi¬ 
tion. Figure 16 shows a test IED just before blast¬ 
ing. The interruption of the wire around the pipe 
gives an electric pulse which is used for triggering 
the transient recorder. In this way we get the inter¬ 
mediate blast wave velocity till its arrival at the 
first pressure transducer. The results, we have ob¬ 
tained from this object are summarized as follows. 
Table 3 shows the intermediate values of the num¬ 
ber of effective fragments and of the maximum 
overpressure, corrected for normal reflection. It 
can be taken from this table that there is no 
significant influence of the different ignition sys¬ 
tems on fragmentation or blast effects, with one 
exception which surprises at first: The blast wave 
of the IED with the booster charge is much weaker 
than in the other cases. The reason is that the high 
order detonation of the booster destroys the con¬ 
tainer wall, before the whole improvised mixture 
comes to reaction. The local variation of the over¬ 
pressure (Figure 17) corresponds to these above 
mentioned results. Besides, the weak effects of the 
moist charges, incidentally detected because of 
rainy weather, are not surprising. 



Figure 16. Test IED (pipe bomb) just before blasting. 

Figure 18 shows the fragmentation distribution 
of this experimental series. In accordance with the 
geometry of the pipe bomb, there are three 
maxima of the fragmentation density: a broad 
one, perpendicular to the axis, and two sharper 
ones in prolongation of it. The minimum of the 
fragmentation probability of this kind of pipe 
bomb can be assumed at an angle of 30 degrees to 
the axis. 


c 

o 


o 

o 

JZ 

</> 

d> 

0) 


o 

£ 

Q) 

i_ 

D 

(/) 

</> 

QJ 


a> 

> 

o 

X 

o 

E 


05 


04 


- 03 


02 


0.1 


0 


o- ignition (photoflash etc.) 
o= initiation (blasting cap) 

8 □- " with booster(5gRDX) 

X- moist charge 

□ 


X 


J_I_L 


8 

8 

x 


l 

X 


1 2 3 4 5 


distance [ml 


Figure 17. Local variation of maximum overpressure of the 
test series with chlorate/sugar charged pipe bombs. 


493 










SUMMARY 



<f 45° 90° 135° 180° 


direction 

Figure 18. Fragmentation distribution of the test series with 
chlorate/sugar charged pipe bombs. 


At Bundeskriminalamt (BKA) methods of 
investigation have been established which can fur¬ 
nish (in a scientific sense) objective measurement 
data on the effects of IEDs (improvised explosive 
devices) on human beings. 

Measurement methods and apparatus for the 
experimental detection of the blast wave and frag¬ 
mentation effects of IEDs are described. The 
problems of providing conditions for carrying out 
suitable studies on explosion effects by means of 
comparative blastings are discussed. Exemplary 
measurement results and their conclusions are pre¬ 
sented. 


Table 3. INTERMEDIATE VALUES OF THE NUMBER OF EFFECTIVE FRAGMENTS AND THE MAXIMUM OVER¬ 
PRESSURE OF THE TEST SERIES WITH CHLORATE/SUGAR CHARGED PIPE BOMBS 


ignition 

system 

effective fragments 
per explosion 
(3m distance, 10% sphere) 

max. overpressure 
(3m distance, 
norm, reflected) 



bar 

psi 

photoflash 

3.5 

0.64 

9.3 

gas lighter (wire bridge) 

4.0 

0.74 

10.7 

fuse head 

2.5 

0.70 

10.2 

blasting cap 

3.25 

0.78 

11.3 

blasting cap with booster (5g RDX) 

3.0 

0.52 

7.5 

[moist charge] 

[0.5] 

[0.18] 

[2.6] 


REFERENCES 

Cohen, E. (1968). Prevention of and protection 
against accidental explosions of munitions, 
fuels and other hazardous mixtures. In: Annals 
of the New York Academy of Sciences (E. M. 
Weyer, ed.) vol. 152, art. 1, New York, pp. 
1-913. 

Diepold, R., Pfoertner, H. and Hommel, H. 
(1970). Sicherheitsabstande bei der lagerung 
und handhabung explosionsfaehiger stoffe. 
Explosivstoffe 18: 25-39. 

French, R. W. and Callender, G. R. (1962). 


Ballistic characteristics of wounding agents. 
In: Wound Ballistics, Office of the Surgeon 
General Department of the Army, Washington 
D.C., pp. 91-141. 

Heiser, R. (1974). Splitterwirkung gegen weiche 
ziele. Fraunhofergesellshaft zur Foerderung der 
angewandten Forschung e.V., Arbeitsgruppe 
fuer ballistische Forschung, Forschungsbericht 
1029, Weil/Rhein. 

Jensen, A. V. (1972). Hazards of chemical rockets 
and propellants handbook, vol. 1. National 
Technical Information Service, U.S. Depart¬ 
ment of Commerce, Springfield, Virginia. 


494 


















SPECIAL PRESENTATION 






































































































































HIGH SPEED PHOTOGRAPHY OF CLANDESTINE 
EXPLOSIVE DEVICES 

Paul M. Dougherty 

San Mateo County Forensic Laboratories 


A motion picture film made in the early 1970’s, 
illustrated the effectiveness of high speed motion 
picture photography in the study of Clandestine 
devices. The contents of the film are shown at two 
different speeds; first at 64 fps, then at any speed 
from 600 fps to 4,800 fps, depending on the event. 

The events are as follows: 

1. Cherry bomb with BB (steel) glued to the 
sides. These were described in the late six¬ 
ties for use in San Francisco against police. 

2. Cherry bomb with tacks glued to sides. 
Again, these were described as used in San 
Francisco in the late sixties. 

3. Bomb made of 2 " x 6" water pipe filled with 
black powder. 

4. Plastic garbage bag with approximately 1 
gallon of gasoline then wrapped with sev¬ 
eral feet of detonating cord. This device was 
reported to have been used in a house in the 
Seattle, Washington area but this could not 
be confirmed at that time. The idea was to 
rig this device to the center of a room, and 
when the light switch was turned on the re¬ 
sulting fireball would envelope and kill who 
was ever in the room. 

5. Homemade Napalm bomb using gasoline 
and Fels Naptha soap. This was initiated by 
a small explosive charge placed on the side 
of the bottle. The flame front’s propagation 
in the gasoline vapor was clearly shown as 
was the spread of the liquid materials. This 
device was used in Berkeley in the late six¬ 
ties or early seventies. 

6. and 7. These were essentially the same de¬ 
vice, champagne bottle base packed with 
C-4 to form a shape charge. In (7) the jet 
from the shape charge can be clearly seen 
on the other side of the target (i.e., car 
door). Even with these crude materials and 
no stand-off an effective shape charge can 
be formed. Explosives other than C-4 may 
be used effectively. 

8. Pipe bomb, 2" x 6", which was somewhat a 


repeat of (3). The ground shock wave was 
clearly visible in this case. 

9. Ammonium nitrate and diesel oil 95:5 by 
weight in a coffee can. The shock wave on 
the ground was visable. Also noted was the 
type of fireball created and the color of the 
smoke. 

10. Telephone pole cut by a C-4 charge. Very 
high velocity type of explosion. 

11. DuPont Jet (shape) Charge used to pene¬ 
trate the sides of oil well casings. The 
detonation of the Primacord was shown in 
contact with the jet charge. 

The following slides were taken as part of an on 
going study on Bomb debris, funded by the Cali¬ 
fornia Council on Criminal Justice (Project 
#0424). These were taken on February 27, 1973, 
for the purpose of added diagnostics regarding the 
reaction history of pipe bombs. 

While two pipe bomb sets were shown, the pic¬ 
tures from one are being printed as typical of the 
series. Photographs are taken from 35 mm slides 
which are frames from a Model 189, Beckman and 
Whitley rotating mirror framing camera. Detona¬ 
tion velocity over the pipe was different for three 
locations on the pipe. This is believed to be due to 
non-uniform pipe wall thickness and non-uniform 
explosive loading density. 

Photograph 1 illustrates the overall set-up to 
photograph at high speed the pipe bomb which is 
in the center of the picture at (A). Above and be¬ 
low it are lights for illumination, these are de¬ 
stroyed by the explosion. The wire entering the 
bomb goes to the SE-1 detonator which is near the 
center of the pipe bomb. The Series shown in 395F 
which consists of a 2" diameter 10" length sched¬ 
ule 40 welded wrought iron pipe with 369 grams of 
Bullseye powder (double base) Det. velocity mea¬ 
sured was 3.9 ± .4 MM/usec. The detonator used 
was an SE1 (high voltage) with Tetryl Pellet.* 

* All photographs in this paper were taken at Lawrence Liver¬ 
more Laboratory, Livermore, CA. and the author wishes to 
thank Mr. Charles A. Honodel and staff for their assistance. 


497 




Figure 5. Time = 32 usee. 


498 




Figure 6. Time 40 usee. 


Figure 7. Time = 56 usee. 


499 






































PAPER WHICH WAS SUBMITTED BUT 
AUTHOR UNABLE TO ATTEND 































































DETECTION OF IMPROVISED EXPLOSIVE DEVICES 
A SYSTEM FOR ENSURING MAIL SAFETY 

Authors: D. W. Williams, K.K.M. Wu, S. R. Silva and J. D. Quinn 


1. BACKGROUND 

The research and development program of the 
Materials Research Laboratories on image recog¬ 
nition commenced with the request from the Aus¬ 
tralian Federal Police for scientific support in the 
area of combating terrorist activities. Of special 
concern to the Federal Police was the detection 
and recognition of improvised explosive devices 
(lED’s), especially in the form of letter or packet 
bombs. A wide range of techniques were consid¬ 
ered. These methods include those dependent 
upon vapour trace detection, atomic or nuclear 
properties, thermal or RF/microwave responses, 
X-ray transmission/fluorescence, electrical prop¬ 
erties of explosives and on chemical or radioactive 
additives to explosives. It was concluded that the 
X-ray fluoroscopy technique was the most suita¬ 
ble. However, the recognition of an IED image de¬ 
pends upon the quality of an operator’s observa¬ 
tion and analysis. It is recognized that such depen¬ 
dency on human involvement is unsatisfactory for 
situations in which a large number of articles need 
to be cleared quickly, i.e. a high throughput situa¬ 
tion. In this type of situation there is a need for 
rapid machine clearance of the bulk of innocuous 
articles, so that only a small percentage of suspect 
articles need to be examined by an operator, 
whose involvement would be required only when 
the machine’s detection/recognition capability 
was exceeded. 

After close examination of IED designs provid¬ 
ed by the police, the Army, postal securities and 
those reported in terrorist literatures ( e.g . “The 
Anarchist’s Cookbook”), we came to the conclu¬ 
sion that a letter- or parcel- detonator (blasting 
cap) with its priming explosive initiator such as 
ASA (lead azide, lead styphnate, aluminum pow¬ 
der). The priming charge being of heavy metal salt 
has a high X-ray attenuation coefficient. In addi¬ 
tion, an effective letter bomb must contain com¬ 
ponents, such as a battery or a mechanical striker, 
to provide the energy required for initiation of the 
detonator. These components usually also have 
high X-ray attenuation coefficients. The attenua¬ 


tion of X-rays through such components effects 
image contrast on a fluorescent screen. Based on 
this knowledge, we have designed two systems, 
System I & II, to automatically screen the mail for 
letter-bombs at high speed. 

The following description deals first with Sys¬ 
tem I, second, with the operational results ob¬ 
tained at CHOGM* using System I, and third with 
the development of System II. 

2. SYSTEM I 

The high volume mail bomb screening device 
(Figure 1) may be described schematically as com¬ 
prising three main functional blocks; first the 
X-ray imaging system which produces an image 
on a fluorescent screen, second, the closed circuit 
television (CCTV) camera, and third, the Real 
Time Video Processor (RTVP) or System I. 

2.1 Hardware 

(a) X-ray Imaging System 

The X-ray imaging system consists of an X-ray 
generator and an X-ray fluorescent screen. Two 
types of screen, a DuPont Cronex E2 screen cover¬ 
ing an area of 250 x 250 mm and a Sirius HSF 
screen of 385 x 285 mm have been used successful¬ 
ly to date. The E2 screen is a fast response, high 
sensitivity type. However, it lacks image sharpness 
when compared to the slower Sirius HSF screen. 
The optium choice of fluorescent screen is related 
to the area to be covered. X-ray energies of be¬ 
tween 80 and 150 kV were the most suitable for 
IED detection, giving good contrast images and 
allowing safe operation. 

A Silicon Intensified Target (SIT) CCTV cam¬ 
era is used to convert the optical image produced 
on the fluorescent screen to an electronic signal. 
The SIT CCTV camera has a bandwidth of 15 
MHz and a line to line resolution of 500 lines. 

(c) Real Time Video Processor 

The technical description of the Real Time Vi- 

* Commonwealth Heads of Government Meeting Held in 
Melbourne 1981. 


503 



OPTICAL 

OBJECT 



Figure 1. Schematic diagram of experimental system. 


deo Processor, RTVP, is shown schematically in 
Figure 3. The Processor consists of six functional 
blocks, labelled 1 to 6 in Figure 2 as follows: 

1. High speed video comparator and keyed 
clamp. 

2. Window generator and clamp driver. 

3. Double field counter. 

4. Dark area counter and digital comparator. 

5. Video synchronizing pulse separator and 
buffer, or Video synchronizing pulse gener¬ 
ator. 

6. Video mixer and selector. 

2.2 Principle of Operation 

A video signal from the CCTV camera is fed to 
the high speed comparator. The comparator level 
is adjustable by the operation of a multiturn po¬ 
tentiometer. The comparator, 1, output consists 
of a stream of information as the video level varies 
above and below the selected threshold level. 
When the video is darker than this preset thresh¬ 
old value an output signal, D, is produced (Figure 
2 ). 

A window generator, 2, activates the area 
counter in the selected area of the picture as 
viewed on the CCTV monitor. This monitored 
area is referred to as the “window”. The size and 


position of this window can be controlled by the 
operator. 

Start signals, S, are fed to the double field 
counter, 3, from either the control input or a man¬ 
ual switch. The area count is zeroed, R, at this 
point. Enable signals are generated by this counter 
for the next two successive fields following either a 
manual or automatic start signal (i.e. one odd and 
one even (raster line) field to make a complete 
frame). 

The dark area counter and comparator, 4, is ac¬ 
tivated only when enable signals from the com¬ 
parator, the window generator and the double 
field counter, F, W, & D, are presented to it simul¬ 
taneously. While activated the area counter counts 
time intervals locally generated by a crystal clock 
and totalizes this count over a complete frame. 
This count is directly proportional to the CCTV 
picture area scanned when enable signals are pres¬ 
ent. A digital comparator then feeds the control 
ports indicating the status of the totalized count 
for the frame, i.e. above or below a present area 
limit. The operator is allowed prior selection of a 
count value above which he requires a control out¬ 
put to hold (or divert) the item, H. Control ports 
are provided for interfacing the start, and hold (or 
divert) signals, with automated handling equip- 


504 










































START 

COUNT 


CAMERA 

VIDEO 



REQUEST 

NEXT 

ITEM 


HOLD 

OR 

DIVERT 

ITEM 


AUX 


VIDEO 

MONITOR 


Figure 2. Schematic diagram of real time video processor. 


. 

■ • Y ' 


%>4 


REAL TIME VIDEO PROCESSOR 



OISPlAY MOQt 
WINDOW DIGITAL 


DREY SCALE 
IHRESHOtO 


ON NORMAL 


CAMERA M0NI10R AUX 


QJ O 




Figure 3. Real time video processor. 


505 



























































ment for parcels, letters, etc. 

Video synchronizing signals are required by the 
double field counter and the window generator. 
These are provided from either the synchronizing 
separator, 5, using the CCTV video, or by a syn¬ 
chronizing pulse generator acting as a master con¬ 
trol for both the CCTV camera and the processor. 

Signals from the video comparator, window 
generator, synchronizing signal, separator genera¬ 
tor and input video buffer are fed to the video 
mixer to provide the following outputs: 

(a) Digital video (darker than the set threshold 
is shown black, remainder shown white). 

(b) Direct camera video (full grey scale). 

The window area may be superimposed on either 
of the selected outputs which are displayed on the 
video monitor. A hold or divert signal is produced 
for an image containing areas darker than the pre¬ 
set grey level and producing counts greater than 
the preset area count. 

To summarize: The composite output from the 
CCTV camera is fed to the comparator system. 
Operating at high speed the comparator provides 
an output signal for areas of the fluorescent screen 
which have luminance less than the preset (grey 
level) threshold. A window area of the fluorescent 
screen is selected to be analyzed, by virtue of com¬ 
mand signals that are generated within the com¬ 
parator. 

The video monitor is able to be switched to dis¬ 
play: 

(i) the CCTV camera video, or 

(ii) the comparator output 

This switching displays the areas of the fluorescent 
screen which are darker than the preset threshold. 
For field operation it is proposed to provide the 
operator with a complete CCTV image (effectively 
of 512 lines of 512 pixels/line) of any item which 
fails to pass the test, and, if required, an alarm to 
draw attention of the operator to the unit. Within 
the selected area of the fluorescent screen the arti¬ 
cle being analysed is readily observed on the moni¬ 
tor. The relationship between counts and area de¬ 
pends upon the magnification factor of fluores¬ 
cent screen image to CCTV image. The require¬ 
ment is to scan a 300 mm x 400 mm image which 
should include the largest standard mail envelope 
of size 285 x 385 mm. Each count will then repre¬ 
sent 0.5 mm 2 of such a field. Present limitations of 
the laboratory equipment allow a window size of 
only 300 x 100 mm. Increase of the window would 
involve the use of shade correction to improve 
image segmentation at the edge. The interconnec¬ 


tion of RTVP with other modules is shown in Fig¬ 
ure 4. 

3. OPERATIONAL TRIAL AT CHOGM 

System I was installed at the CHOGM mail se¬ 
curity centre with the Australian Federal Police 
mail checking equipment which included a Line 
Scan System and a Torrex II Fluoroscopic Inspec¬ 
tion System, both of the Scan Ray Corporation, 
and several vapour trace detectors (VTD). 

3.1 Procedures 

Mail delivered by Australia Post was first ex¬ 
amined by the Line Scan and, depending on 
whether identification was established, was fol¬ 
lowed by fluoroscopic and VTD checks. Further 
checks were carried out by System I. The Police 
equipment (apart from VTD’s) required visual 
examination and image interpretation by obser¬ 
vers trained in bomb recognition, whereas System 
I could clear or reject mail automatically. 

3.2 Mail Statistics 

A total of nearly 8000 mail items was checked. 
The numbers and categories of items accepted or 
rejected by System I are given in Table 1. Rejec¬ 
tion is on the basis of an X-ray density equal to or 
greater than that of a minimum size bomb which 
would be capable of causing significant injury (1). 
Rejected items are divided into two categories in 
the Table—Category A (non-stationery) consist¬ 
ing of miscellaneous articles such as corkscrews, 
scissors, keys, cassettes, etc.) and Category B 
items (stationery). Respective values as a percen¬ 
tage of total mail items are 0.6% and 1.8%. 

System I controls were set to clear individual 
items at a ratio of two per second. This rate could 
be increased by an order of magnitude by the 
stacking of mail items. However, the clearance 
rate as set was more than adequate for the 
throughput involved. 

The stop signal which interrupts the power sup¬ 
ply to the conveyor belt motor was spuriously acti¬ 
vated by electrical noise on three occasions. The 
origin of noise and its mode of progagation 
through the equipment was determined and the 
noise was subsequently eliminated. 

3.3 Detection of Concealed Objects 

Shortly after the commencement of mail check¬ 
ing, it became apparent that Category A items 
could present a detection problem—the conceal¬ 
ment, whether by accident or design, of an explo¬ 
sive device by an identifiable innocuous object of 


506 





Figure 4. RTVP with layout for continuous monitoring. 


Table 1. MAIL CLEARED OR REJECTED BY SYSTEM I 


Description 

Number 

Percentage of total 

Mail Processed 

7824 

100% 

Mail Cleared 

7634 

97.6% 

Mail Rejected (Category A) 

Miscellaneous articles 

22 


Keys 

24 


Cassettes 

4 


Sub-total 

50 

0.6% 

Mail Rejected (Category B) 

Stacks of letters 

6 


Books and paper 

44 


Paper Rolls and Staples 

21 


Clips or fasteners 

66 


noise 

3 


Sub-Total 

140 

1.8% 

TOTAL 

190 

2.4% 


507 










































sufficient area and X-ray density. The capability 
of System I to display a binary image for a varia¬ 
ble threshold may be varied to reveal intensity dif¬ 
ferences which cannot otherwise be discerned by 
human vision. To our knowledge no other system 
used for mail inspection has this capability. 

3.4 Discussion of Results 

Percentage clearance and rejection values given 
in Table 1 show that System I cleared 97.6% of 
mail free of IED’s as safe. The system can there¬ 
fore be regarded as a ‘stand alone’ system when 
employed in a mail registry situation handling up 
to a few thousand articles daily. The 2.4% of the 
mail which cannot be cleared by the system need 
then be examined fluoroscopically by an observer. 
However, in the case of a major mail exchange 
where the throughput requirement may reach 
60,000 articles per hour, with a daily volume well 
exceeding one million, the small percentage of sus¬ 
pect articles would still amount to a large volume 
and need to be cleared at the rate of 1440 articles 
per hour in order to avoid serious back log. 

Table 1 showed that the three quarters of the 
mail rejected by the System—1.8% of the total— 
contained various types of stationery items includ¬ 
ing large metal paper clips and paper fasteners 
(Category B). It is envisaged that these items may 
be automatically identified, and subsequently 
cleared, by a system with pattern recognition 
capability, leaving only the remainder, 0.6% of 
the mail (Category A), to an observer for further 
inspection. For a throughput rate of 60,000 arti¬ 
cles per hour, this is equivalent to 360 articles per 
hour—a rate easily manageable by observers. It is 
therefore adjustifiable on the basis of these statis¬ 
tics to upgrade System I by incorporating a micro¬ 
processor to give the required pattern recognition 
capability. 

An additional justification would be that of 
providing further capability in the recognition of a 
particular bomb design(s). This could be of advan¬ 
tage in the provision of quick response to a partic¬ 
ular bomb threat by a known design through the 
insertion of parametric data into a recognition al¬ 
gorithm designed for this purpose. The upgraded 
system is known as System II. 

4. SYSTEM II 

Figure 5 is a schematic diagram showing the ba¬ 
sic arrangement of equipment and the manner of 
linking the equipment to the multibus of the single 
board computer utilized for the purpose of carry¬ 
ing out the pattern recognition. 


CAMERA 



Figure 5. Schematic diagram of system II. 


4.1 Image Acquisition 

Figure 6 is a block diagram of the image acquisi¬ 
tion system. The video signal from the CCTV 
camera is processed by the ‘comparator’ into bin¬ 
ary data according to a preselected threshold in¬ 
tensity level as in System I. The output signal is 
then processed by the Encoder Board into run-end 
code data. The horizontal position of each transi¬ 
tion, from white to black or vice versa, along a 
fine during the raster scan is inserted into the word 
generated at the end of each line. Since the TV 
raster scan is composed of two consecutive inter¬ 
laced field of 256 lines each, an image is thus re¬ 
corded in the form of a 512 x 512 matrix. 

A large reduction in the quantity of data to be 
stored, hence the overall data transfer rate, may 
be achieved through run-end coding. Neverthe¬ 
less, each word is generated in a minimum time of 
120 nanosecond and needs to be stored at this rate. 
This is handled by the High Speed RAM Buffer 
Board, which incorporates two identical high 
speed IK x 1 word Intel-2115A static ram boards, 
in the manner described below. 


508 






















Figure 6. Block circuitry of the image acquisition system. 


(1) As the data is generated, it flows into the 
First Buffer. When this is filled, the 16 bit data 
path is immediately switched to the input of the 
Second Buffer. 

(2) In the same time as the data is flowing into 
the second Buffer, the data temporarily stored in 
the First Buffer is transferred by a direct memory 
access circuit to the memory of the central proc¬ 
essing unit, an Intel 86/12 single board computer. 

(3) When the Second Buffer is filled, the input 
data path is switched back to the First Buffer. By 
this time, the data in the First Buffer would have 
been emptied into the memory of the CPU. 

(4) The process continues until the completion 
of the interlaced picture scan. 

4.2 Image Analysis 

At the completion of data transfer, the 8086 mi¬ 
croprocessor of the computer is activated to begin 
analysis of the image. The data of transition pairs 
are rearranged to form a 512 line single frame 
from the two 256 line half frames. Overlapping 



Figure 7. Algorithm for the clearance of paper clips. 


pairs on successive lines are then grouped to form 
individual objects by a component labelling algo¬ 
rithm. The algorithm is based on that of 
run-tracking, which is particularly suitable for 
image data in run-end coded form. The runs are 
located sequentially from left to right along each 
line, each run is treated as belonging to a new ob¬ 
ject, thus given a new label. The labels which are 
usually whole numbers start with 1 then continue 
in ascending order according to the order in which 
the objects are encountered. On the second and 
subsequent lines, each run is subjected to an over¬ 
lap search to determine whether it overlaps with 
any run on the preceding line. The run is assigned 
a new, hitherto unused label, if there is no over¬ 
lap. But, if there is overlap, it is given the same la¬ 
bel as the run it overlapped. The overlap search is 
continued to determine whether it also overlaps 
with the next run on the preceding line. If there is 
more overlap, and the runs are of different labels, 
the run with the higher number is relabelled with 
the lower number. 


509 















































































































4.3 Feature measurement 

The identification of objects is to be based on 
shape information independent of size and orien¬ 
tation. Geometrical features which are readily ex¬ 
tracted from the image and which may be comput¬ 
er in a single pass during the labelling process are 
chosen. The more exotic shape descriptors such as 
the Fourier descriptor and differential chain code 
are not preferred because they would require 
images with well defined boundaries and would in¬ 
volve greater computational effort. The features 
we have computed include area, perimeter, mo¬ 
ments about a fixed point, vertical and horizontal 
Feret diameter, and secondary features such as 
centroid, circularity and central moments. 

4.4 Algorithm For Clearance of Paper Clips 

The automatic mail clearance is referred to as 
IED detection. The automatic identification of let¬ 
ter bombs is extremely difficult if not impossible, 
since there is no standard bomb design. Although 
there may be essential bomb components such as a 
detonator and energy source, yet they come in var¬ 
ious size, shape and are assembled differently. In 
addition to this, the probability of a letter contain¬ 
ing IED is extremely low. Even if we can design a 
set of detection criterion to cover a wide range of 
IED configurations, the application of the criter¬ 
ion to every letter in search of virtually non-exis¬ 
tent item is inefficient. The present strategy is to 
discriminate a limited variety of stationery items 
from other articles based on their geometrical fea¬ 
tures. The requirement is therefore to identify 
those characteristic features of these items which 
are not possessed by essential components of IED, 
i.e. the detonator and the energy source. Any mail 
containing items which cannot be cleared accord¬ 
ing to those features, must be treated as suspect 
and inspected by a human operator or by more so¬ 
phisticated techniques. 

A preliminary scheme for the clearance of mail 
containing paper clips is presented as an example 
in the flow chart of Figure 7. This basis of adopt¬ 
ing each criterion is explained below:— 

Criterion 1 

Objects below a minimum size, Ai, may be dis¬ 
regarded. It is designed to eliminate noise and 
fragments of image close to the intensity thresh¬ 
old. The minimum size is chosen to be well below 
the size of items such as the priming charge of a 
detonator, blob of solder in electronic circuits, 
electric wire junctions, etc. 


Criterion 2 

Mail containing items over a maximum size, A 2 , 
are not cleared. A : is set to be the size of the larg¬ 
est paper clip designed to be cleared. 

Criterion 3 

All paper clips are characterized by a small val¬ 
ue of circulatory, C, coupled with a large value of 
area normalised moment of intertia, I. In particu¬ 
lar, the C of paper clips are much lower than those 
of compact items. Therefore, we may clear items 
with C below, say, 0.1 as paper clips. 

Criterion 4 

When the image of paper clips is fragmented 
through thresholding the C of fragmented parts 
can be greater than the value 0.1 used in Criterion 
3. These fragments often appear as bar-like items 
with a length to width ratio, a/b, greater than 5. 
This corresponds to values C < 0.436 and I > 
0.433. Because the fragments are much narrower 
than other compact items with the same a/b ratio, 
their area counts are comparatively much lower. 
Thus, items of size below certain value, A 3 , and 
with C < 0.436 coupled with I > 0.433, may be 
cleared as fragments of paper clips. 

The choice of quantities A,, A 2 , and A 3 ap¬ 
peared in the above criteria is dependent upon the 
exposure and threshold conditions, and should be 
subject to field trials. 

4.5 Performance 

At the time of reporting, System II has not been 
fully tested. The image acquisition system de¬ 
scribed in Section 4.1, however, has been tested. It 
can successfully store images in run-end code 
form in 1/25 second—two consecutive interlaced 
half TV frames. The image analysis algorithms 
have also been tested and proven. The speed of 
analysis is dependent upon the complexity of an 
image. It took an average of 5 seconds to analyse 
images with 1000 transition points using an LSI 
11/2 processor with programmes written in For¬ 
tran. This speed could be increased at least five 
times on a faster 86/12A processor. Hence, Sys¬ 
tem II could be capable of achieving a throughput 
rate of approximately 3600 articles per hour which 
exceeds the rate of 1440 articles per hour required 
for processing all mail rejected by System I in the 
mail exchange situation. 

We have tried the clearance scheme (Section 
4.4) on images of simulated mail containing 
various types of paper clips at several intensity 
threshold levels and on images of simulated IED 


510 


of the types detected by Australian and British 
postal authorities. The results indicated that paper 
clips could be cleared as safe in over 90% of the 
cases, whereas not a single IED component ana¬ 
lyzed was cleared as safe. 

5. SUMMARY 

We have developed the basis for two systems for 
automatic screening of mail for letter bombs at 
high speed. The first system, System I, employs a 
closed circuit television camera for viewing the 
fluoroscopic image. The video signal from the 
camera is passed through a ‘comparator’ provid¬ 
ing an output signal for regions of the fluorescent 
screen which are darker than a preselected in¬ 
tensity threshold. The output is then fed to the 
gate input of a counter/timer, which provides a 
measure of the total duration of the signal in one 
TV raster scan, indicating the extent of the darker 
areas of the image. A letter is cleared as being safe 
when the extent of the dark areas is less than a pre¬ 
selected threshold corresponding to the minimum 
size bomb considered to be effective. 

It has been established from trial at the 
CHOGM in Melbourne 1981, that 97.6% of the 
mail received contained only paper and small 
paper clips, pins and staples. It was possible to set 
the threshold levels of the system so as to clear 
these letters as being safe while rejecting without 
failure those containing as little as a single deto¬ 
nator as being unsafe. The system makes decisions 
in real time, however, a practical system will be 
limited by the throughput rate of the feeding 
mechanism. During the trial a rate of two items 


per second was achieved with a simple conveyor 
belt. System I can be regarded as a ‘stand alone’ 
system when employed in a large mail Registry sit¬ 
uation handling say up to 1000 articles daily. The 
2.4% or so of the mail which cannot be cleared by 
the system may then be examined fluoroscopically 
by an observer. 

A second system, System II, has been developed 
in experimental form to clear stationery items us¬ 
ing pattern recognition techniques. It is esentially 
System I with the addition of a microprocessor, 
Intel 86/12 single board computer. The signal out¬ 
put from System I is processed by the Encoder 
Board into run-end code data, which is then 
stored in the CPU by High Speed RAM Buffer 
Board. The whole process takes 1/25 second, two 
half frames. The segmentation of images and the 
determination of geometrical attributes of the seg¬ 
mented objects may be achieved in approximately 
one second. System II has not been engineered 
fully or tested in an operational environment. 
However, we have tested a clearance scheme on 
images of various types of paper clips at several in¬ 
tensity threshold levels, and on images of simu¬ 
lated IED’s. The scheme was capable of clearing 
paper clips as safe in over 90% of the cases, 
whereas it did not clear as safe a single IED com¬ 
ponent tested. 

REFERENCE 

/. Lidstone, D. P. Letter Bombs: A guide for the 

layman Forensic Explosives Laboratory, 

R.A.R.D.E., Royal Arsenal East, London. 

Prepared 1972. 


* U.S. GOVERNMENT PRINTING OFFICE: 1984-426-295 


511 







































































































































H 312 85 
























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